diff --git a/archive.c b/archive.c
index f4331aeb49..c95e398152 100644
--- a/archive.c
+++ b/archive.c
@@ -312,7 +312,7 @@ int write_archive_entries(struct archiver_args *args,
 	struct object_id fake_oid;
 	int i;
 
-	oidcpy(&fake_oid, null_oid());
+	oidcpy(&fake_oid, null_oid(the_hash_algo));
 
 	if (args->baselen > 0 && args->base[args->baselen - 1] == '/') {
 		size_t len = args->baselen;
diff --git a/blame.c b/blame.c
index a15ddf9333..703dab43e7 100644
--- a/blame.c
+++ b/blame.c
@@ -255,7 +255,7 @@ static struct commit *fake_working_tree_commit(struct repository *r,
 		switch (st.st_mode & S_IFMT) {
 		case S_IFREG:
 			if (opt->flags.allow_textconv &&
-			    textconv_object(r, read_from, mode, null_oid(), 0, &buf_ptr, &buf_len))
+			    textconv_object(r, read_from, mode, null_oid(the_hash_algo), 0, &buf_ptr, &buf_len))
 				strbuf_attach(&buf, buf_ptr, buf_len, buf_len + 1);
 			else if (strbuf_read_file(&buf, read_from, st.st_size) != st.st_size)
 				die_errno("cannot open or read '%s'", read_from);
diff --git a/branch.c b/branch.c
index 91297d55ac..6d01d7d6bd 100644
--- a/branch.c
+++ b/branch.c
@@ -633,7 +633,7 @@ void create_branch(struct repository *r,
 						  0, &err);
 	if (!transaction ||
 		ref_transaction_update(transaction, ref.buf,
-					&oid, forcing ? NULL : null_oid(),
+					&oid, forcing ? NULL : null_oid(the_hash_algo),
 					NULL, NULL, flags, msg, &err) ||
 		ref_transaction_commit(transaction, &err))
 		die("%s", err.buf);
diff --git a/builtin/checkout.c b/builtin/checkout.c
index 01ea9ff8b2..2e7486cf65 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -130,8 +130,8 @@ static int post_checkout_hook(struct commit *old_commit, struct commit *new_comm
 			      int changed)
 {
 	return run_hooks_l(the_repository, "post-checkout",
-			   oid_to_hex(old_commit ? &old_commit->object.oid : null_oid()),
-			   oid_to_hex(new_commit ? &new_commit->object.oid : null_oid()),
+			   oid_to_hex(old_commit ? &old_commit->object.oid : null_oid(the_hash_algo)),
+			   oid_to_hex(new_commit ? &new_commit->object.oid : null_oid(the_hash_algo)),
 			   changed ? "1" : "0", NULL);
 	/* "new_commit" can be NULL when checking out from the index before
 	   a commit exists. */
@@ -710,7 +710,7 @@ static int reset_tree(struct tree *tree, const struct checkout_opts *o,
 	opts.src_index = the_repository->index;
 	opts.dst_index = the_repository->index;
 	init_checkout_metadata(&opts.meta, info->refname,
-			       info->commit ? &info->commit->object.oid : null_oid(),
+			       info->commit ? &info->commit->object.oid : null_oid(the_hash_algo),
 			       NULL);
 	if (parse_tree(tree) < 0)
 		return 128;
diff --git a/builtin/clone.c b/builtin/clone.c
index f14229abf4..36aba65e06 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -690,7 +690,7 @@ static int checkout(int submodule_progress, int filter_submodules,
 	if (write_locked_index(the_repository->index, &lock_file, COMMIT_LOCK))
 		die(_("unable to write new index file"));
 
-	err |= run_hooks_l(the_repository, "post-checkout", oid_to_hex(null_oid()),
+	err |= run_hooks_l(the_repository, "post-checkout", oid_to_hex(null_oid(the_hash_algo)),
 			   oid_to_hex(&oid), "1", NULL);
 
 	if (!err && (option_recurse_submodules.nr > 0)) {
diff --git a/builtin/describe.c b/builtin/describe.c
index e2e73f3d75..23df333fd0 100644
--- a/builtin/describe.c
+++ b/builtin/describe.c
@@ -518,7 +518,7 @@ static void describe_blob(struct object_id oid, struct strbuf *dst)
 {
 	struct rev_info revs;
 	struct strvec args = STRVEC_INIT;
-	struct process_commit_data pcd = { *null_oid(), oid, dst, &revs};
+	struct process_commit_data pcd = { *null_oid(the_hash_algo), oid, dst, &revs};
 
 	strvec_pushl(&args, "internal: The first arg is not parsed",
 		     "--objects", "--in-commit-order", "--reverse", "HEAD",
diff --git a/builtin/diff.c b/builtin/diff.c
index a4fffee42c..fa963808c3 100644
--- a/builtin/diff.c
+++ b/builtin/diff.c
@@ -104,7 +104,7 @@ static void builtin_diff_b_f(struct rev_info *revs,
 
 	stuff_change(&revs->diffopt,
 		     blob[0]->mode, canon_mode(st.st_mode),
-		     &blob[0]->item->oid, null_oid(),
+		     &blob[0]->item->oid, null_oid(the_hash_algo),
 		     1, 0,
 		     blob[0]->path ? blob[0]->path : path,
 		     path);
@@ -498,7 +498,8 @@ int cmd_diff(int argc,
 
 	/* If this is a no-index diff, just run it and exit there. */
 	if (no_index)
-		exit(diff_no_index(&rev, no_index == DIFF_NO_INDEX_IMPLICIT,
+		exit(diff_no_index(&rev, the_repository->hash_algo,
+				   no_index == DIFF_NO_INDEX_IMPLICIT,
 				   argc, argv));
 
 
diff --git a/builtin/fast-export.c b/builtin/fast-export.c
index a5c82eef1d..7a5c2925cd 100644
--- a/builtin/fast-export.c
+++ b/builtin/fast-export.c
@@ -869,7 +869,7 @@ static void handle_tag(const char *name, struct tag *tag)
 				p = rewrite_commit((struct commit *)tagged);
 				if (!p) {
 					printf("reset %s\nfrom %s\n\n",
-					       name, oid_to_hex(null_oid()));
+					       name, oid_to_hex(null_oid(the_hash_algo)));
 					free(buf);
 					return;
 				}
@@ -883,7 +883,7 @@ static void handle_tag(const char *name, struct tag *tag)
 
 	if (tagged->type == OBJ_TAG) {
 		printf("reset %s\nfrom %s\n\n",
-		       name, oid_to_hex(null_oid()));
+		       name, oid_to_hex(null_oid(the_hash_algo)));
 	}
 	skip_prefix(name, "refs/tags/", &name);
 	printf("tag %s\n", name);
@@ -1023,7 +1023,7 @@ static void handle_tags_and_duplicates(struct string_list *extras)
 				 * it.
 				 */
 				printf("reset %s\nfrom %s\n\n",
-				       name, oid_to_hex(null_oid()));
+				       name, oid_to_hex(null_oid(the_hash_algo)));
 				continue;
 			}
 
@@ -1042,7 +1042,7 @@ static void handle_tags_and_duplicates(struct string_list *extras)
 				if (!reference_excluded_commits) {
 					/* delete the ref */
 					printf("reset %s\nfrom %s\n\n",
-					       name, oid_to_hex(null_oid()));
+					       name, oid_to_hex(null_oid(the_hash_algo)));
 					continue;
 				}
 				/* set ref to commit using oid, not mark */
@@ -1153,7 +1153,7 @@ static void handle_deletes(void)
 			continue;
 
 		printf("reset %s\nfrom %s\n\n",
-				refspec->dst, oid_to_hex(null_oid()));
+				refspec->dst, oid_to_hex(null_oid(the_hash_algo)));
 	}
 }
 
diff --git a/builtin/fsck.c b/builtin/fsck.c
index 62c7494bbd..f86ecd8eaa 100644
--- a/builtin/fsck.c
+++ b/builtin/fsck.c
@@ -625,7 +625,7 @@ static int fsck_loose(const struct object_id *oid, const char *path, void *data)
 	void *contents = NULL;
 	int eaten;
 	struct object_info oi = OBJECT_INFO_INIT;
-	struct object_id real_oid = *null_oid();
+	struct object_id real_oid = *null_oid(the_hash_algo);
 	int err = 0;
 
 	strbuf_reset(&cb_data->obj_type);
diff --git a/builtin/grep.c b/builtin/grep.c
index cbbf6f2643..283d64cab8 100644
--- a/builtin/grep.c
+++ b/builtin/grep.c
@@ -453,7 +453,7 @@ static int grep_submodule(struct grep_opt *opt,
 		return 0;
 
 	subrepo = xmalloc(sizeof(*subrepo));
-	if (repo_submodule_init(subrepo, superproject, path, null_oid())) {
+	if (repo_submodule_init(subrepo, superproject, path, null_oid(opt->repo->hash_algo))) {
 		free(subrepo);
 		return 0;
 	}
diff --git a/builtin/ls-files.c b/builtin/ls-files.c
index a4431429b7..7bc418be5d 100644
--- a/builtin/ls-files.c
+++ b/builtin/ls-files.c
@@ -234,7 +234,8 @@ static void show_submodule(struct repository *superproject,
 {
 	struct repository subrepo;
 
-	if (repo_submodule_init(&subrepo, superproject, path, null_oid()))
+	if (repo_submodule_init(&subrepo, superproject, path,
+				null_oid(superproject->hash_algo)))
 		return;
 
 	if (repo_read_index(&subrepo) < 0)
diff --git a/builtin/rebase.c b/builtin/rebase.c
index d4715ed35d..1cd802dd92 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -925,7 +925,7 @@ static void fill_branch_base(struct rebase_options *options,
 				 options->orig_head, &merge_bases) < 0)
 		exit(128);
 	if (!merge_bases || merge_bases->next)
-		oidcpy(branch_base, null_oid());
+		oidcpy(branch_base, null_oid(the_hash_algo));
 	else
 		oidcpy(branch_base, &merge_bases->item->object.oid);
 
diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index 7b28fc9df6..b3e2a9d0c6 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -363,7 +363,7 @@ static void write_head_info(void)
 	strvec_clear(&excludes_vector);
 
 	if (!sent_capabilities)
-		show_ref("capabilities^{}", null_oid());
+		show_ref("capabilities^{}", null_oid(the_hash_algo));
 
 	advertise_shallow_grafts(1);
 
diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
index c1a8029714..570226ea16 100644
--- a/builtin/submodule--helper.c
+++ b/builtin/submodule--helper.c
@@ -78,7 +78,7 @@ static int get_default_remote_submodule(const char *module_path, char **default_
 	int ret;
 
 	if (repo_submodule_init(&subrepo, the_repository, module_path,
-				null_oid()) < 0)
+				null_oid(the_hash_algo)) < 0)
 		return die_message(_("could not get a repository handle for submodule '%s'"),
 				   module_path);
 	ret = repo_get_default_remote(&subrepo, default_remote);
@@ -308,7 +308,7 @@ static void runcommand_in_submodule_cb(const struct cache_entry *list_item,
 	displaypath = get_submodule_displaypath(path, info->prefix,
 						info->super_prefix);
 
-	sub = submodule_from_path(the_repository, null_oid(), path);
+	sub = submodule_from_path(the_repository, null_oid(the_hash_algo), path);
 
 	if (!sub)
 		die(_("No url found for submodule path '%s' in .gitmodules"),
@@ -468,7 +468,7 @@ static void init_submodule(const char *path, const char *prefix,
 
 	displaypath = get_submodule_displaypath(path, prefix, super_prefix);
 
-	sub = submodule_from_path(the_repository, null_oid(), path);
+	sub = submodule_from_path(the_repository, null_oid(the_hash_algo), path);
 
 	if (!sub)
 		die(_("No url found for submodule path '%s' in .gitmodules"),
@@ -645,14 +645,14 @@ static void status_submodule(const char *path, const struct object_id *ce_oid,
 	if (validate_submodule_path(path) < 0)
 		exit(128);
 
-	if (!submodule_from_path(the_repository, null_oid(), path))
+	if (!submodule_from_path(the_repository, null_oid(the_hash_algo), path))
 		die(_("no submodule mapping found in .gitmodules for path '%s'"),
 		      path);
 
 	displaypath = get_submodule_displaypath(path, prefix, super_prefix);
 
 	if ((CE_STAGEMASK & ce_flags) >> CE_STAGESHIFT) {
-		print_status(flags, 'U', path, null_oid(), displaypath);
+		print_status(flags, 'U', path, null_oid(the_hash_algo), displaypath);
 		goto cleanup;
 	}
 
@@ -912,7 +912,7 @@ static void generate_submodule_summary(struct summary_cb *info,
 	struct strbuf errmsg = STRBUF_INIT;
 	int total_commits = -1;
 
-	if (!info->cached && oideq(&p->oid_dst, null_oid())) {
+	if (!info->cached && oideq(&p->oid_dst, null_oid(the_hash_algo))) {
 		if (S_ISGITLINK(p->mod_dst)) {
 			struct ref_store *refs = repo_get_submodule_ref_store(the_repository,
 									      p->sm_path);
@@ -1051,7 +1051,7 @@ static void prepare_submodule_summary(struct summary_cb *info,
 
 		if (info->for_status && p->status != 'A' &&
 		    (sub = submodule_from_path(the_repository,
-					       null_oid(), p->sm_path))) {
+					       null_oid(the_hash_algo), p->sm_path))) {
 			char *config_key = NULL;
 			const char *value;
 			int ignore_all = 0;
@@ -1259,7 +1259,7 @@ static void sync_submodule(const char *path, const char *prefix,
 	if (validate_submodule_path(path) < 0)
 		exit(128);
 
-	sub = submodule_from_path(the_repository, null_oid(), path);
+	sub = submodule_from_path(the_repository, null_oid(the_hash_algo), path);
 
 	if (sub && sub->url) {
 		if (starts_with_dot_dot_slash(sub->url) ||
@@ -1404,7 +1404,7 @@ static void deinit_submodule(const char *path, const char *prefix,
 	if (validate_submodule_path(path) < 0)
 		exit(128);
 
-	sub = submodule_from_path(the_repository, null_oid(), path);
+	sub = submodule_from_path(the_repository, null_oid(the_hash_algo), path);
 
 	if (!sub || !sub->name)
 		goto cleanup;
@@ -1929,7 +1929,7 @@ static int determine_submodule_update_strategy(struct repository *r,
 					       enum submodule_update_type update,
 					       struct submodule_update_strategy *out)
 {
-	const struct submodule *sub = submodule_from_path(r, null_oid(), path);
+	const struct submodule *sub = submodule_from_path(r, null_oid(the_hash_algo), path);
 	char *key;
 	const char *val;
 	int ret;
@@ -2089,7 +2089,7 @@ static int prepare_to_clone_next_submodule(const struct cache_entry *ce,
 		goto cleanup;
 	}
 
-	sub = submodule_from_path(the_repository, null_oid(), ce->name);
+	sub = submodule_from_path(the_repository, null_oid(the_hash_algo), ce->name);
 
 	if (!sub) {
 		next_submodule_warn_missing(suc, out, displaypath);
@@ -2485,7 +2485,7 @@ static int remote_submodule_branch(const char *path, const char **branch)
 	char *key;
 	*branch = NULL;
 
-	sub = submodule_from_path(the_repository, null_oid(), path);
+	sub = submodule_from_path(the_repository, null_oid(the_hash_algo), path);
 	if (!sub)
 		return die_message(_("could not initialize submodule at path '%s'"),
 				   path);
@@ -2531,7 +2531,7 @@ static int ensure_core_worktree(const char *path)
 	const char *cw;
 	struct repository subrepo;
 
-	if (repo_submodule_init(&subrepo, the_repository, path, null_oid()))
+	if (repo_submodule_init(&subrepo, the_repository, path, null_oid(the_hash_algo)))
 		return die_message(_("could not get a repository handle for submodule '%s'"),
 				   path);
 
@@ -2644,7 +2644,7 @@ static int update_submodule(struct update_data *update_data)
 		return ret;
 
 	if (update_data->just_cloned)
-		oidcpy(&update_data->suboid, null_oid());
+		oidcpy(&update_data->suboid, null_oid(the_hash_algo));
 	else if (repo_resolve_gitlink_ref(the_repository, update_data->sm_path,
 					  "HEAD", &update_data->suboid))
 		return die_message(_("Unable to find current revision in submodule path '%s'"),
@@ -2697,8 +2697,8 @@ static int update_submodule(struct update_data *update_data)
 		struct update_data next = *update_data;
 
 		next.prefix = NULL;
-		oidcpy(&next.oid, null_oid());
-		oidcpy(&next.suboid, null_oid());
+		oidcpy(&next.oid, null_oid(the_hash_algo));
+		oidcpy(&next.suboid, null_oid(the_hash_algo));
 
 		cp.dir = update_data->sm_path;
 		cp.git_cmd = 1;
@@ -3057,7 +3057,7 @@ static int module_set_url(int argc, const char **argv, const char *prefix,
 	if (argc != 2 || !(path = argv[0]) || !(newurl = argv[1]))
 		usage_with_options(usage, options);
 
-	sub = submodule_from_path(the_repository, null_oid(), path);
+	sub = submodule_from_path(the_repository, null_oid(the_hash_algo), path);
 
 	if (!sub)
 		die(_("no submodule mapping found in .gitmodules for path '%s'"),
@@ -3113,7 +3113,7 @@ static int module_set_branch(int argc, const char **argv, const char *prefix,
 	if (argc != 1 || !(path = argv[0]))
 		usage_with_options(usage, options);
 
-	sub = submodule_from_path(the_repository, null_oid(), path);
+	sub = submodule_from_path(the_repository, null_oid(the_hash_algo), path);
 
 	if (!sub)
 		die(_("no submodule mapping found in .gitmodules for path '%s'"),
diff --git a/builtin/unpack-objects.c b/builtin/unpack-objects.c
index e20c120913..73d431a0dd 100644
--- a/builtin/unpack-objects.c
+++ b/builtin/unpack-objects.c
@@ -505,7 +505,7 @@ static void unpack_delta_entry(enum object_type type, unsigned long delta_size,
 			 * has not been resolved yet.
 			 */
 			oidclr(&obj_list[nr].oid, the_repository->hash_algo);
-			add_delta_to_list(nr, null_oid(), base_offset,
+			add_delta_to_list(nr, null_oid(the_hash_algo), base_offset,
 					  delta_data, delta_size);
 			return;
 		}
diff --git a/builtin/update-ref.c b/builtin/update-ref.c
index 4d35bdc4b4..3796b9844d 100644
--- a/builtin/update-ref.c
+++ b/builtin/update-ref.c
@@ -500,7 +500,7 @@ static void parse_cmd_symref_verify(struct ref_transaction *transaction,
 	 */
 	old_target = parse_next_refname(&next);
 	if (!old_target)
-		oidcpy(&old_oid, null_oid());
+		oidcpy(&old_oid, null_oid(the_hash_algo));
 
 	if (*next != line_termination)
 		die("symref-verify %s: extra input: %s", refname, next);
diff --git a/builtin/worktree.c b/builtin/worktree.c
index 48448a8355..87ccd47794 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -578,7 +578,7 @@ done:
 
 		strvec_pushl(&opt.env, "GIT_DIR", "GIT_WORK_TREE", NULL);
 		strvec_pushl(&opt.args,
-			     oid_to_hex(null_oid()),
+			     oid_to_hex(null_oid(the_hash_algo)),
 			     oid_to_hex(&commit->object.oid),
 			     "1",
 			     NULL);
diff --git a/combine-diff.c b/combine-diff.c
index 9527f3160d..553bf59fed 100644
--- a/combine-diff.c
+++ b/combine-diff.c
@@ -1066,7 +1066,7 @@ static void show_patch_diff(struct combine_diff_path *elem, int num_parent,
 						   &result_size, NULL, NULL);
 		} else if (textconv) {
 			struct diff_filespec *df = alloc_filespec(elem->path);
-			fill_filespec(df, null_oid(), 0, st.st_mode);
+			fill_filespec(df, null_oid(the_hash_algo), 0, st.st_mode);
 			result_size = fill_textconv(opt->repo, textconv, df, &result);
 			free_filespec(df);
 		} else if (0 <= (fd = open(elem->path, O_RDONLY))) {
diff --git a/diff-lib.c b/diff-lib.c
index 353b473ed5..244468dd1a 100644
--- a/diff-lib.c
+++ b/diff-lib.c
@@ -172,7 +172,7 @@ void run_diff_files(struct rev_info *revs, unsigned int option)
 			 * these from (stage - 2).
 			 */
 			dpath = combine_diff_path_new(ce->name, ce_namelen(ce),
-						      wt_mode, null_oid(), 2);
+						      wt_mode, null_oid(the_hash_algo), 2);
 
 			while (i < entries) {
 				struct cache_entry *nce = istate->cache[i];
@@ -257,7 +257,7 @@ void run_diff_files(struct rev_info *revs, unsigned int option)
 				   ce_intent_to_add(ce)) {
 				newmode = ce_mode_from_stat(ce, st.st_mode);
 				diff_addremove(&revs->diffopt, '+', newmode,
-					       null_oid(), 0, ce->name, 0);
+					       null_oid(the_hash_algo), 0, ce->name, 0);
 				continue;
 			}
 
@@ -274,7 +274,7 @@ void run_diff_files(struct rev_info *revs, unsigned int option)
 		}
 		oldmode = ce->ce_mode;
 		old_oid = &ce->oid;
-		new_oid = changed ? null_oid() : &ce->oid;
+		new_oid = changed ? null_oid(the_hash_algo) : &ce->oid;
 		diff_change(&revs->diffopt, oldmode, newmode,
 			    old_oid, new_oid,
 			    !is_null_oid(old_oid),
@@ -330,7 +330,7 @@ static int get_stat_data(const struct cache_entry *ce,
 						    0, dirty_submodule);
 		if (changed) {
 			mode = ce_mode_from_stat(ce, st.st_mode);
-			oid = null_oid();
+			oid = null_oid(the_hash_algo);
 		}
 	}
 
@@ -402,7 +402,7 @@ static int show_modified(struct rev_info *revs,
 
 		p = combine_diff_path_new(new_entry->name,
 					  ce_namelen(new_entry),
-					  mode, null_oid(), 2);
+					  mode, null_oid(the_hash_algo), 2);
 		p->parent[0].status = DIFF_STATUS_MODIFIED;
 		p->parent[0].mode = new_entry->ce_mode;
 		oidcpy(&p->parent[0].oid, &new_entry->oid);
diff --git a/diff-no-index.c b/diff-no-index.c
index 6f277892d3..9739b2b268 100644
--- a/diff-no-index.c
+++ b/diff-no-index.c
@@ -113,7 +113,8 @@ static void populate_from_stdin(struct diff_filespec *s)
 	populate_common(s, &buf);
 }
 
-static struct diff_filespec *noindex_filespec(const char *name, int mode,
+static struct diff_filespec *noindex_filespec(const struct git_hash_algo *algop,
+					      const char *name, int mode,
 					      enum special special)
 {
 	struct diff_filespec *s;
@@ -121,7 +122,7 @@ static struct diff_filespec *noindex_filespec(const char *name, int mode,
 	if (!name)
 		name = "/dev/null";
 	s = alloc_filespec(name);
-	fill_filespec(s, null_oid(), 0, mode);
+	fill_filespec(s, null_oid(algop), 0, mode);
 	if (special == SPECIAL_STDIN)
 		populate_from_stdin(s);
 	else if (special == SPECIAL_PIPE)
@@ -129,7 +130,7 @@ static struct diff_filespec *noindex_filespec(const char *name, int mode,
 	return s;
 }
 
-static int queue_diff(struct diff_options *o,
+static int queue_diff(struct diff_options *o, const struct git_hash_algo *algop,
 		      const char *name1, const char *name2, int recursing)
 {
 	int mode1 = 0, mode2 = 0;
@@ -145,14 +146,14 @@ static int queue_diff(struct diff_options *o,
 
 		if (S_ISDIR(mode1)) {
 			/* 2 is file that is created */
-			d1 = noindex_filespec(NULL, 0, SPECIAL_NONE);
-			d2 = noindex_filespec(name2, mode2, special2);
+			d1 = noindex_filespec(algop, NULL, 0, SPECIAL_NONE);
+			d2 = noindex_filespec(algop, name2, mode2, special2);
 			name2 = NULL;
 			mode2 = 0;
 		} else {
 			/* 1 is file that is deleted */
-			d1 = noindex_filespec(name1, mode1, special1);
-			d2 = noindex_filespec(NULL, 0, SPECIAL_NONE);
+			d1 = noindex_filespec(algop, name1, mode1, special1);
+			d2 = noindex_filespec(algop, NULL, 0, SPECIAL_NONE);
 			name1 = NULL;
 			mode1 = 0;
 		}
@@ -217,7 +218,7 @@ static int queue_diff(struct diff_options *o,
 				n2 = buffer2.buf;
 			}
 
-			ret = queue_diff(o, n1, n2, 1);
+			ret = queue_diff(o, algop, n1, n2, 1);
 		}
 		string_list_clear(&p1, 0);
 		string_list_clear(&p2, 0);
@@ -234,8 +235,8 @@ static int queue_diff(struct diff_options *o,
 			SWAP(special1, special2);
 		}
 
-		d1 = noindex_filespec(name1, mode1, special1);
-		d2 = noindex_filespec(name2, mode2, special2);
+		d1 = noindex_filespec(algop, name1, mode1, special1);
+		d2 = noindex_filespec(algop, name2, mode2, special2);
 		diff_queue(&diff_queued_diff, d1, d2);
 		return 0;
 	}
@@ -297,9 +298,8 @@ static const char * const diff_no_index_usage[] = {
 	NULL
 };
 
-int diff_no_index(struct rev_info *revs,
-		  int implicit_no_index,
-		  int argc, const char **argv)
+int diff_no_index(struct rev_info *revs, const struct git_hash_algo *algop,
+		  int implicit_no_index, int argc, const char **argv)
 {
 	int i, no_index;
 	int ret = 1;
@@ -354,7 +354,7 @@ int diff_no_index(struct rev_info *revs,
 	setup_diff_pager(&revs->diffopt);
 	revs->diffopt.flags.exit_with_status = 1;
 
-	if (queue_diff(&revs->diffopt, paths[0], paths[1], 0))
+	if (queue_diff(&revs->diffopt, algop, paths[0], paths[1], 0))
 		goto out;
 	diff_set_mnemonic_prefix(&revs->diffopt, "1/", "2/");
 	diffcore_std(&revs->diffopt);
diff --git a/diff.c b/diff.c
index 4f802b4251..4ce5933a44 100644
--- a/diff.c
+++ b/diff.c
@@ -4346,7 +4346,7 @@ static struct diff_tempfile *prepare_temp_file(struct repository *r,
 				die_errno("readlink(%s)", one->path);
 			prep_temp_blob(r->index, one->path, temp, sb.buf, sb.len,
 				       (one->oid_valid ?
-					&one->oid : null_oid()),
+					&one->oid : null_oid(the_hash_algo)),
 				       (one->oid_valid ?
 					one->mode : S_IFLNK));
 			strbuf_release(&sb);
@@ -4355,7 +4355,7 @@ static struct diff_tempfile *prepare_temp_file(struct repository *r,
 			/* we can borrow from the file in the work tree */
 			temp->name = one->path;
 			if (!one->oid_valid)
-				oid_to_hex_r(temp->hex, null_oid());
+				oid_to_hex_r(temp->hex, null_oid(the_hash_algo));
 			else
 				oid_to_hex_r(temp->hex, &one->oid);
 			/* Even though we may sometimes borrow the
@@ -6649,8 +6649,8 @@ static void create_filepairs_for_header_only_notifications(struct diff_options *
 
 			one = alloc_filespec(e->key);
 			two = alloc_filespec(e->key);
-			fill_filespec(one, null_oid(), 0, 0);
-			fill_filespec(two, null_oid(), 0, 0);
+			fill_filespec(one, null_oid(the_hash_algo), 0, 0);
+			fill_filespec(two, null_oid(the_hash_algo), 0, 0);
 			p = diff_queue(q, one, two);
 			p->status = DIFF_STATUS_MODIFIED;
 		}
diff --git a/diff.h b/diff.h
index 0a566f5531..0822111c62 100644
--- a/diff.h
+++ b/diff.h
@@ -656,7 +656,7 @@ void flush_one_hunk(struct object_id *result, struct git_hash_ctx *ctx);
 
 int diff_result_code(struct rev_info *);
 
-int diff_no_index(struct rev_info *,
+int diff_no_index(struct rev_info *, const struct git_hash_algo *algop,
 		  int implicit_no_index, int, const char **);
 
 int index_differs_from(struct repository *r, const char *def,
diff --git a/dir.c b/dir.c
index cbd82be6c9..28b0e03feb 100644
--- a/dir.c
+++ b/dir.c
@@ -4035,7 +4035,7 @@ static void connect_wt_gitdir_in_nested(const char *sub_worktree,
 			 */
 			i++;
 
-		sub = submodule_from_path(&subrepo, null_oid(), ce->name);
+		sub = submodule_from_path(&subrepo, null_oid(the_hash_algo), ce->name);
 		if (!sub || !is_submodule_active(&subrepo, ce->name))
 			/* .gitmodules broken or inactive sub */
 			continue;
diff --git a/grep.c b/grep.c
index 4e155ee9e6..9284b5741f 100644
--- a/grep.c
+++ b/grep.c
@@ -1517,7 +1517,7 @@ static int fill_textconv_grep(struct repository *r,
 		fill_filespec(df, gs->identifier, 1, 0100644);
 		break;
 	case GREP_SOURCE_FILE:
-		fill_filespec(df, null_oid(), 0, 0100644);
+		fill_filespec(df, null_oid(r->hash_algo), 0, 0100644);
 		break;
 	default:
 		BUG("attempt to textconv something without a path?");
diff --git a/hash.c b/hash.c
index 4d9f98f72c..4a04ecb50e 100644
--- a/hash.c
+++ b/hash.c
@@ -1,5 +1,3 @@
-#define USE_THE_REPOSITORY_VARIABLE
-
 #include "git-compat-util.h"
 #include "hash.h"
 #include "hex.h"
@@ -232,9 +230,9 @@ const struct git_hash_algo hash_algos[GIT_HASH_NALGOS] = {
 	}
 };
 
-const struct object_id *null_oid(void)
+const struct object_id *null_oid(const struct git_hash_algo *algop)
 {
-	return the_hash_algo->null_oid;
+	return algop->null_oid;
 }
 
 const char *empty_tree_oid_hex(const struct git_hash_algo *algop)
diff --git a/hash.h b/hash.h
index 55d67ed83f..a9ef76fc8e 100644
--- a/hash.h
+++ b/hash.h
@@ -340,7 +340,7 @@ static inline int hash_algo_by_ptr(const struct git_hash_algo *p)
 
 const struct git_hash_algo *unsafe_hash_algo(const struct git_hash_algo *algop);
 
-const struct object_id *null_oid(void);
+const struct object_id *null_oid(const struct git_hash_algo *algop);
 
 static inline int hashcmp(const unsigned char *sha1, const unsigned char *sha2, const struct git_hash_algo *algop)
 {
diff --git a/log-tree.c b/log-tree.c
index 8b184d6776..5dd1b63076 100644
--- a/log-tree.c
+++ b/log-tree.c
@@ -499,7 +499,7 @@ void log_write_email_headers(struct rev_info *opt, struct commit *commit,
 {
 	struct strbuf headers = STRBUF_INIT;
 	const char *name = oid_to_hex(opt->zero_commit ?
-				      null_oid() : &commit->object.oid);
+				      null_oid(the_hash_algo) : &commit->object.oid);
 
 	*need_8bit_cte_p = 0; /* unknown */
 
diff --git a/merge-ort.c b/merge-ort.c
index 46e78c3ffa..eb3a834652 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -1817,7 +1817,7 @@ static int merge_submodule(struct merge_options *opt,
 		BUG("submodule deleted on one side; this should be handled outside of merge_submodule()");
 
 	if ((sub_not_initialized = repo_submodule_init(&subrepo,
-		opt->repo, path, null_oid()))) {
+		opt->repo, path, null_oid(the_hash_algo)))) {
 		path_msg(opt, CONFLICT_SUBMODULE_NOT_INITIALIZED, 0,
 			 path, NULL, NULL, NULL,
 			 _("Failed to merge submodule %s (not checked out)"),
@@ -2199,7 +2199,7 @@ static int handle_content_merge(struct merge_options *opt,
 		two_way = ((S_IFMT & o->mode) != (S_IFMT & a->mode));
 
 		merge_status = merge_3way(opt, path,
-					  two_way ? null_oid() : &o->oid,
+					  two_way ? null_oid(the_hash_algo) : &o->oid,
 					  &a->oid, &b->oid,
 					  pathnames, extra_marker_size,
 					  &result_buf);
@@ -2231,7 +2231,7 @@ static int handle_content_merge(struct merge_options *opt,
 	} else if (S_ISGITLINK(a->mode)) {
 		int two_way = ((S_IFMT & o->mode) != (S_IFMT & a->mode));
 		clean = merge_submodule(opt, pathnames[0],
-					two_way ? null_oid() : &o->oid,
+					two_way ? null_oid(the_hash_algo) : &o->oid,
 					&a->oid, &b->oid, &result->oid);
 		if (clean < 0)
 			return -1;
@@ -2739,7 +2739,7 @@ static void apply_directory_rename_modifications(struct merge_options *opt,
 		assert(!new_ci->match_mask);
 		new_ci->dirmask = 0;
 		new_ci->stages[1].mode = 0;
-		oidcpy(&new_ci->stages[1].oid, null_oid());
+		oidcpy(&new_ci->stages[1].oid, null_oid(the_hash_algo));
 
 		/*
 		 * Now that we have the file information in new_ci, make sure
@@ -2752,7 +2752,7 @@ static void apply_directory_rename_modifications(struct merge_options *opt,
 				continue;
 			/* zero out any entries related to files */
 			ci->stages[i].mode = 0;
-			oidcpy(&ci->stages[i].oid, null_oid());
+			oidcpy(&ci->stages[i].oid, null_oid(the_hash_algo));
 		}
 
 		/* Now we want to focus on new_ci, so reassign ci to it. */
@@ -3122,7 +3122,7 @@ static int process_renames(struct merge_options *opt,
 			if (type_changed) {
 				/* rename vs. typechange */
 				/* Mark the original as resolved by removal */
-				memcpy(&oldinfo->stages[0].oid, null_oid(),
+				memcpy(&oldinfo->stages[0].oid, null_oid(the_hash_algo),
 				       sizeof(oldinfo->stages[0].oid));
 				oldinfo->stages[0].mode = 0;
 				oldinfo->filemask &= 0x06;
@@ -3994,7 +3994,7 @@ static int process_entry(struct merge_options *opt,
 			if (ci->filemask & (1 << i))
 				continue;
 			ci->stages[i].mode = 0;
-			oidcpy(&ci->stages[i].oid, null_oid());
+			oidcpy(&ci->stages[i].oid, null_oid(the_hash_algo));
 		}
 	} else if (ci->df_conflict && ci->merged.result.mode != 0) {
 		/*
@@ -4041,7 +4041,7 @@ static int process_entry(struct merge_options *opt,
 				continue;
 			/* zero out any entries related to directories */
 			new_ci->stages[i].mode = 0;
-			oidcpy(&new_ci->stages[i].oid, null_oid());
+			oidcpy(&new_ci->stages[i].oid, null_oid(the_hash_algo));
 		}
 
 		/*
@@ -4163,11 +4163,11 @@ static int process_entry(struct merge_options *opt,
 			new_ci->merged.result.mode = ci->stages[2].mode;
 			oidcpy(&new_ci->merged.result.oid, &ci->stages[2].oid);
 			new_ci->stages[1].mode = 0;
-			oidcpy(&new_ci->stages[1].oid, null_oid());
+			oidcpy(&new_ci->stages[1].oid, null_oid(the_hash_algo));
 			new_ci->filemask = 5;
 			if ((S_IFMT & b_mode) != (S_IFMT & o_mode)) {
 				new_ci->stages[0].mode = 0;
-				oidcpy(&new_ci->stages[0].oid, null_oid());
+				oidcpy(&new_ci->stages[0].oid, null_oid(the_hash_algo));
 				new_ci->filemask = 4;
 			}
 
@@ -4175,11 +4175,11 @@ static int process_entry(struct merge_options *opt,
 			ci->merged.result.mode = ci->stages[1].mode;
 			oidcpy(&ci->merged.result.oid, &ci->stages[1].oid);
 			ci->stages[2].mode = 0;
-			oidcpy(&ci->stages[2].oid, null_oid());
+			oidcpy(&ci->stages[2].oid, null_oid(the_hash_algo));
 			ci->filemask = 3;
 			if ((S_IFMT & a_mode) != (S_IFMT & o_mode)) {
 				ci->stages[0].mode = 0;
-				oidcpy(&ci->stages[0].oid, null_oid());
+				oidcpy(&ci->stages[0].oid, null_oid(the_hash_algo));
 				ci->filemask = 2;
 			}
 
@@ -4304,7 +4304,7 @@ static int process_entry(struct merge_options *opt,
 		/* Deleted on both sides */
 		ci->merged.is_null = 1;
 		ci->merged.result.mode = 0;
-		oidcpy(&ci->merged.result.oid, null_oid());
+		oidcpy(&ci->merged.result.oid, null_oid(the_hash_algo));
 		assert(!ci->df_conflict);
 		ci->merged.clean = !ci->path_conflict;
 	}
diff --git a/merge-recursive.c b/merge-recursive.c
index 884ccf99a5..9aedffc546 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -502,7 +502,7 @@ static int get_tree_entry_if_blob(struct repository *r,
 
 	ret = get_tree_entry(r, tree, path, &dfs->oid, &dfs->mode);
 	if (S_ISDIR(dfs->mode)) {
-		oidcpy(&dfs->oid, null_oid());
+		oidcpy(&dfs->oid, null_oid(the_hash_algo));
 		dfs->mode = 0;
 	}
 	return ret;
@@ -1238,7 +1238,7 @@ static int merge_submodule(struct merge_options *opt,
 	if (is_null_oid(b))
 		return 0;
 
-	if (repo_submodule_init(&subrepo, opt->repo, path, null_oid())) {
+	if (repo_submodule_init(&subrepo, opt->repo, path, null_oid(the_hash_algo))) {
 		output(opt, 1, _("Failed to merge submodule %s (not checked out)"), path);
 		return 0;
 	}
@@ -1698,7 +1698,7 @@ static int handle_file_collision(struct merge_options *opt,
 
 	/* Store things in diff_filespecs for functions that need it */
 	null.path = (char *)collide_path;
-	oidcpy(&null.oid, null_oid());
+	oidcpy(&null.oid, null_oid(the_hash_algo));
 	null.mode = 0;
 
 	if (merge_mode_and_contents(opt, &null, a, b, collide_path,
@@ -2897,14 +2897,14 @@ static int process_renames(struct merge_options *opt,
 			dst_other.mode = ren1->dst_entry->stages[other_stage].mode;
 			try_merge = 0;
 
-			if (oideq(&src_other.oid, null_oid()) &&
+			if (oideq(&src_other.oid, null_oid(the_hash_algo)) &&
 			    ren1->dir_rename_original_type == 'A') {
 				setup_rename_conflict_info(RENAME_VIA_DIR,
 							   opt, ren1, NULL);
 			} else if (renamed_to_self) {
 				setup_rename_conflict_info(RENAME_NORMAL,
 							   opt, ren1, NULL);
-			} else if (oideq(&src_other.oid, null_oid())) {
+			} else if (oideq(&src_other.oid, null_oid(the_hash_algo))) {
 				setup_rename_conflict_info(RENAME_DELETE,
 							   opt, ren1, NULL);
 			} else if ((dst_other.mode == ren1->pair->two->mode) &&
@@ -2923,7 +2923,7 @@ static int process_renames(struct merge_options *opt,
 						      1, /* update_cache */
 						      0  /* update_wd    */))
 					clean_merge = -1;
-			} else if (!oideq(&dst_other.oid, null_oid())) {
+			} else if (!oideq(&dst_other.oid, null_oid(the_hash_algo))) {
 				/*
 				 * Probably not a clean merge, but it's
 				 * premature to set clean_merge to 0 here,
diff --git a/notes-merge.c b/notes-merge.c
index 67a472020d..5008faef45 100644
--- a/notes-merge.c
+++ b/notes-merge.c
@@ -617,7 +617,7 @@ int notes_merge(struct notes_merge_options *o,
 	if (repo_get_merge_bases(the_repository, local, remote, &bases) < 0)
 		exit(128);
 	if (!bases) {
-		base_oid = null_oid();
+		base_oid = null_oid(the_hash_algo);
 		base_tree_oid = the_hash_algo->empty_tree;
 		if (o->verbosity >= 4)
 			printf("No merge base found; doing history-less merge\n");
diff --git a/notes.c b/notes.c
index f534423050..ce5a1006a8 100644
--- a/notes.c
+++ b/notes.c
@@ -1353,7 +1353,7 @@ int copy_note(struct notes_tree *t,
 	if (note)
 		return add_note(t, to_obj, note, combine_notes);
 	else if (existing_note)
-		return add_note(t, to_obj, null_oid(), combine_notes);
+		return add_note(t, to_obj, null_oid(the_hash_algo), combine_notes);
 
 	return 0;
 }
diff --git a/object-file.c b/object-file.c
index de603e2ca8..772c311f18 100644
--- a/object-file.c
+++ b/object-file.c
@@ -2405,7 +2405,7 @@ static int index_mem(struct index_state *istate,
 
 		opts.strict = 1;
 		opts.error_func = hash_format_check_report;
-		if (fsck_buffer(null_oid(), type, buf, size, &opts))
+		if (fsck_buffer(null_oid(the_hash_algo), type, buf, size, &opts))
 			die(_("refusing to create malformed object"));
 		fsck_finish(&opts);
 	}
diff --git a/parse-options-cb.c b/parse-options-cb.c
index 166d35e0eb..50c8afe412 100644
--- a/parse-options-cb.c
+++ b/parse-options-cb.c
@@ -145,7 +145,7 @@ int parse_opt_object_id(const struct option *opt, const char *arg, int unset)
 	struct object_id *target = opt->value;
 
 	if (unset) {
-		oidcpy(target, null_oid());
+		oidcpy(target, null_oid(the_hash_algo));
 		return 0;
 	}
 	if (!arg)
diff --git a/range-diff.c b/range-diff.c
index 9501c358a8..8a2dcbee32 100644
--- a/range-diff.c
+++ b/range-diff.c
@@ -467,7 +467,7 @@ static struct diff_filespec *get_filespec(const char *name, const char *p)
 {
 	struct diff_filespec *spec = alloc_filespec(name);
 
-	fill_filespec(spec, null_oid(), 0, 0100644);
+	fill_filespec(spec, null_oid(the_hash_algo), 0, 0100644);
 	spec->data = (char *)p;
 	spec->size = strlen(p);
 	spec->should_munmap = 0;
diff --git a/read-cache.c b/read-cache.c
index a012cb2236..2f9e21c897 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1735,7 +1735,7 @@ static int verify_hdr(const struct cache_header *hdr, unsigned long size)
 	end = (unsigned char *)hdr + size;
 	start = end - the_hash_algo->rawsz;
 	oidread(&oid, start, the_repository->hash_algo);
-	if (oideq(&oid, null_oid()))
+	if (oideq(&oid, null_oid(the_hash_algo)))
 		return 0;
 
 	the_hash_algo->init_fn(&c);
diff --git a/refs.c b/refs.c
index 118465271d..215294115b 100644
--- a/refs.c
+++ b/refs.c
@@ -1377,7 +1377,7 @@ int ref_transaction_create(struct ref_transaction *transaction,
 		return 1;
 	}
 	return ref_transaction_update(transaction, refname, new_oid,
-				      null_oid(), new_target, NULL, flags,
+				      null_oid(the_hash_algo), new_target, NULL, flags,
 				      msg, err);
 }
 
@@ -1396,7 +1396,7 @@ int ref_transaction_delete(struct ref_transaction *transaction,
 	if (old_target && !(flags & REF_NO_DEREF))
 		BUG("delete cannot operate on symrefs with deref mode");
 	return ref_transaction_update(transaction, refname,
-				      null_oid(), old_oid,
+				      null_oid(the_hash_algo), old_oid,
 				      NULL, old_target, flags,
 				      msg, err);
 }
@@ -2160,7 +2160,7 @@ struct ref_store *repo_get_submodule_ref_store(struct repository *repo,
 	subrepo = xmalloc(sizeof(*subrepo));
 
 	if (repo_submodule_init(subrepo, repo, submodule,
-				null_oid())) {
+				null_oid(the_hash_algo))) {
 		free(subrepo);
 		goto done;
 	}
@@ -2345,14 +2345,14 @@ static int run_transaction_hook(struct ref_transaction *transaction,
 		strbuf_reset(&buf);
 
 		if (!(update->flags & REF_HAVE_OLD))
-			strbuf_addf(&buf, "%s ", oid_to_hex(null_oid()));
+			strbuf_addf(&buf, "%s ", oid_to_hex(null_oid(the_hash_algo)));
 		else if (update->old_target)
 			strbuf_addf(&buf, "ref:%s ", update->old_target);
 		else
 			strbuf_addf(&buf, "%s ", oid_to_hex(&update->old_oid));
 
 		if (!(update->flags & REF_HAVE_NEW))
-			strbuf_addf(&buf, "%s ", oid_to_hex(null_oid()));
+			strbuf_addf(&buf, "%s ", oid_to_hex(null_oid(the_hash_algo)));
 		else if (update->new_target)
 			strbuf_addf(&buf, "ref:%s ", update->new_target);
 		else
@@ -2794,7 +2794,7 @@ static int migrate_one_ref(const char *refname, const char *referent UNUSED, con
 		if (ret < 0)
 			goto done;
 
-		ret = ref_transaction_update(data->transaction, refname, NULL, null_oid(),
+		ret = ref_transaction_update(data->transaction, refname, NULL, null_oid(the_hash_algo),
 					     symref_target.buf, NULL,
 					     REF_SKIP_CREATE_REFLOG | REF_NO_DEREF, NULL, data->errbuf);
 		if (ret < 0)
diff --git a/refs/debug.c b/refs/debug.c
index fbc4df08b4..7c61b775e4 100644
--- a/refs/debug.c
+++ b/refs/debug.c
@@ -217,7 +217,7 @@ static int debug_read_raw_ref(struct ref_store *ref_store, const char *refname,
 	struct debug_ref_store *drefs = (struct debug_ref_store *)ref_store;
 	int res = 0;
 
-	oidcpy(oid, null_oid());
+	oidcpy(oid, null_oid(ref_store->repo->hash_algo));
 	res = drefs->refs->be->read_raw_ref(drefs->refs, refname, oid, referent,
 					    type, failure_errno);
 
diff --git a/refs/files-backend.c b/refs/files-backend.c
index 6c6e67dc1c..ba31cfdb93 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -1270,7 +1270,7 @@ static void prune_ref(struct files_ref_store *refs, struct ref_to_prune *r)
 	ref_transaction_add_update(
 			transaction, r->name,
 			REF_NO_DEREF | REF_HAVE_NEW | REF_HAVE_OLD | REF_IS_PRUNING,
-			null_oid(), &r->oid, NULL, NULL, NULL, NULL);
+			null_oid(the_hash_algo), &r->oid, NULL, NULL, NULL, NULL);
 	if (ref_transaction_commit(transaction, &err))
 		goto cleanup;
 
diff --git a/reset.c b/reset.c
index b22b1be792..bb59027181 100644
--- a/reset.c
+++ b/reset.c
@@ -80,7 +80,7 @@ static int update_refs(const struct reset_head_opts *opts,
 	}
 	if (!ret && run_hook)
 		run_hooks_l(the_repository, "post-checkout",
-			    oid_to_hex(head ? head : null_oid()),
+			    oid_to_hex(head ? head : null_oid(the_hash_algo)),
 			    oid_to_hex(oid), "1", NULL);
 	strbuf_release(&msg);
 	return ret;
diff --git a/sequencer.c b/sequencer.c
index ad0ab75c8d..c112d2e1c4 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -265,8 +265,8 @@ static struct update_ref_record *init_update_ref_record(const char *ref)
 
 	CALLOC_ARRAY(rec, 1);
 
-	oidcpy(&rec->before, null_oid());
-	oidcpy(&rec->after, null_oid());
+	oidcpy(&rec->before, null_oid(the_hash_algo));
+	oidcpy(&rec->after, null_oid(the_hash_algo));
 
 	/* This may fail, but that's fine, we will keep the null OID. */
 	refs_read_ref(get_main_ref_store(the_repository), ref, &rec->before);
@@ -667,7 +667,7 @@ static int fast_forward_to(struct repository *r,
 	if (!transaction ||
 	    ref_transaction_update(transaction, "HEAD",
 				   to, unborn && !is_rebase_i(opts) ?
-				   null_oid() : from, NULL, NULL,
+				   null_oid(the_hash_algo) : from, NULL, NULL,
 				   0, sb.buf, &err) ||
 	    ref_transaction_commit(transaction, &err)) {
 		ref_transaction_free(transaction);
@@ -1301,7 +1301,7 @@ int update_head_with_reflog(const struct commit *old_head,
 						  0, err);
 	if (!transaction ||
 	    ref_transaction_update(transaction, "HEAD", new_head,
-				   old_head ? &old_head->object.oid : null_oid(),
+				   old_head ? &old_head->object.oid : null_oid(the_hash_algo),
 				   NULL, NULL, 0, sb.buf, err) ||
 	    ref_transaction_commit(transaction, err)) {
 		ret = -1;
@@ -4683,7 +4683,7 @@ static void create_autostash_internal(struct repository *r,
 			write_file(path, "%s", oid_to_hex(&oid));
 		} else {
 			refs_update_ref(get_main_ref_store(r), "", refname,
-					&oid, null_oid(), 0, UPDATE_REFS_DIE_ON_ERR);
+					&oid, null_oid(the_hash_algo), 0, UPDATE_REFS_DIE_ON_ERR);
 		}
 
 		printf(_("Created autostash: %s\n"), buf.buf);
diff --git a/submodule-config.c b/submodule-config.c
index a25059ed7f..d82b404b73 100644
--- a/submodule-config.c
+++ b/submodule-config.c
@@ -831,7 +831,7 @@ static int gitmodules_cb(const char *var, const char *value,
 
 	parameter.cache = repo->submodule_cache;
 	parameter.treeish_name = NULL;
-	parameter.gitmodules_oid = null_oid();
+	parameter.gitmodules_oid = null_oid(the_hash_algo);
 	parameter.overwrite = 1;
 
 	return parse_config(var, value, ctx, &parameter);
diff --git a/submodule.c b/submodule.c
index 0530e8cf24..0821507eca 100644
--- a/submodule.c
+++ b/submodule.c
@@ -124,7 +124,7 @@ int update_path_in_gitmodules(const char *oldpath, const char *newpath)
 	if (is_gitmodules_unmerged(the_repository->index))
 		die(_("Cannot change unmerged .gitmodules, resolve merge conflicts first"));
 
-	submodule = submodule_from_path(the_repository, null_oid(), oldpath);
+	submodule = submodule_from_path(the_repository, null_oid(the_hash_algo), oldpath);
 	if (!submodule || !submodule->name) {
 		warning(_("Could not find section in .gitmodules where path=%s"), oldpath);
 		return -1;
@@ -153,7 +153,7 @@ int remove_path_from_gitmodules(const char *path)
 	if (is_gitmodules_unmerged(the_repository->index))
 		die(_("Cannot change unmerged .gitmodules, resolve merge conflicts first"));
 
-	submodule = submodule_from_path(the_repository, null_oid(), path);
+	submodule = submodule_from_path(the_repository, null_oid(the_hash_algo), path);
 	if (!submodule || !submodule->name) {
 		warning(_("Could not find section in .gitmodules where path=%s"), path);
 		return -1;
@@ -204,7 +204,7 @@ void set_diffopt_flags_from_submodule_config(struct diff_options *diffopt,
 					     const char *path)
 {
 	const struct submodule *submodule = submodule_from_path(the_repository,
-								null_oid(),
+								null_oid(the_hash_algo),
 								path);
 	if (submodule) {
 		const char *ignore;
@@ -312,7 +312,7 @@ int is_tree_submodule_active(struct repository *repo,
 
 int is_submodule_active(struct repository *repo, const char *path)
 {
-	return is_tree_submodule_active(repo, null_oid(), path);
+	return is_tree_submodule_active(repo, null_oid(the_hash_algo), path);
 }
 
 int is_submodule_populated_gently(const char *path, int *return_error_code)
@@ -778,7 +778,7 @@ const struct submodule *submodule_from_ce(const struct cache_entry *ce)
 	if (!should_update_submodules())
 		return NULL;
 
-	return submodule_from_path(the_repository, null_oid(), ce->name);
+	return submodule_from_path(the_repository, null_oid(the_hash_algo), ce->name);
 }
 
 
@@ -1062,7 +1062,7 @@ static int submodule_needs_pushing(struct repository *r,
 				   const char *path,
 				   struct oid_array *commits)
 {
-	if (!submodule_has_commits(r, path, null_oid(), commits))
+	if (!submodule_has_commits(r, path, null_oid(the_hash_algo), commits))
 		/*
 		 * NOTE: We do consider it safe to return "no" here. The
 		 * correct answer would be "We do not know" instead of
@@ -1126,7 +1126,7 @@ int find_unpushed_submodules(struct repository *r,
 		const struct submodule *submodule;
 		const char *path = NULL;
 
-		submodule = submodule_from_name(r, null_oid(), name->string);
+		submodule = submodule_from_name(r, null_oid(the_hash_algo), name->string);
 		if (submodule)
 			path = submodule->path;
 		else
@@ -1351,7 +1351,7 @@ static void calculate_changed_submodule_paths(struct repository *r,
 		const struct submodule *submodule;
 		const char *path = NULL;
 
-		submodule = submodule_from_name(r, null_oid(), name->string);
+		submodule = submodule_from_name(r, null_oid(the_hash_algo), name->string);
 		if (submodule)
 			path = submodule->path;
 		else
@@ -1360,7 +1360,7 @@ static void calculate_changed_submodule_paths(struct repository *r,
 		if (!path)
 			continue;
 
-		if (submodule_has_commits(r, path, null_oid(), &cs_data->new_commits)) {
+		if (submodule_has_commits(r, path, null_oid(the_hash_algo), &cs_data->new_commits)) {
 			changed_submodule_data_clear(cs_data);
 			*name->string = '\0';
 		}
@@ -1602,7 +1602,7 @@ get_fetch_task_from_index(struct submodule_parallel_fetch *spf,
 		if (!S_ISGITLINK(ce->ce_mode))
 			continue;
 
-		task = fetch_task_create(spf, ce->name, null_oid());
+		task = fetch_task_create(spf, ce->name, null_oid(the_hash_algo));
 		if (!task)
 			continue;
 
@@ -2166,7 +2166,7 @@ int submodule_move_head(const char *path, const char *super_prefix,
 	if (old_head && !is_submodule_populated_gently(path, error_code_ptr))
 		return 0;
 
-	sub = submodule_from_path(the_repository, null_oid(), path);
+	sub = submodule_from_path(the_repository, null_oid(the_hash_algo), path);
 
 	if (!sub)
 		BUG("could not get submodule information for '%s'", path);
@@ -2376,7 +2376,7 @@ static void relocate_single_git_dir_into_superproject(const char *path,
 
 	real_old_git_dir = real_pathdup(old_git_dir, 1);
 
-	sub = submodule_from_path(the_repository, null_oid(), path);
+	sub = submodule_from_path(the_repository, null_oid(the_hash_algo), path);
 	if (!sub)
 		die(_("could not lookup name for submodule '%s'"), path);
 
@@ -2462,7 +2462,7 @@ void absorb_git_dir_into_superproject(const char *path,
 		* superproject did not rewrite the git file links yet,
 		* fix it now.
 		*/
-		sub = submodule_from_path(the_repository, null_oid(), path);
+		sub = submodule_from_path(the_repository, null_oid(the_hash_algo), path);
 		if (!sub)
 			die(_("could not lookup name for submodule '%s'"), path);
 		submodule_name_to_gitdir(&sub_gitdir, the_repository, sub->name);
@@ -2594,7 +2594,7 @@ int submodule_to_gitdir(struct repository *repo,
 		strbuf_addstr(buf, git_dir);
 	}
 	if (!is_git_directory(buf->buf)) {
-		sub = submodule_from_path(repo, null_oid(), submodule);
+		sub = submodule_from_path(repo, null_oid(the_hash_algo), submodule);
 		if (!sub) {
 			ret = -1;
 			goto cleanup;
diff --git a/t/helper/test-ref-store.c b/t/helper/test-ref-store.c
index e00fce592b..2ff67c067a 100644
--- a/t/helper/test-ref-store.c
+++ b/t/helper/test-ref-store.c
@@ -179,7 +179,7 @@ static int cmd_for_each_ref__exclude(struct ref_store *refs, const char **argv)
 
 static int cmd_resolve_ref(struct ref_store *refs, const char **argv)
 {
-	struct object_id oid = *null_oid();
+	struct object_id oid = *null_oid(the_hash_algo);
 	const char *refname = notnull(*argv++, "refname");
 	int resolve_flags = arg_flags(*argv++, "resolve-flags", empty_flags);
 	int flags;
diff --git a/t/helper/test-submodule-nested-repo-config.c b/t/helper/test-submodule-nested-repo-config.c
index 6dce957153..2710341cd5 100644
--- a/t/helper/test-submodule-nested-repo-config.c
+++ b/t/helper/test-submodule-nested-repo-config.c
@@ -21,7 +21,7 @@ int cmd__submodule_nested_repo_config(int argc, const char **argv)
 
 	setup_git_directory();
 
-	if (repo_submodule_init(&subrepo, the_repository, argv[1], null_oid())) {
+	if (repo_submodule_init(&subrepo, the_repository, argv[1], null_oid(the_hash_algo))) {
 		die_usage(argv, "Submodule not found.");
 	}
 
diff --git a/tree-diff.c b/tree-diff.c
index 60c558c2b5..e00fc2f450 100644
--- a/tree-diff.c
+++ b/tree-diff.c
@@ -181,7 +181,7 @@ static void emit_path(struct combine_diff_path ***tail,
 
 		strbuf_add(base, path, pathlen);
 		p = combine_diff_path_new(base->buf, base->len, mode,
-					  oid ? oid : null_oid(),
+					  oid ? oid : null_oid(the_hash_algo),
 					  nparent);
 		strbuf_setlen(base, old_baselen);
 
@@ -206,7 +206,7 @@ static void emit_path(struct combine_diff_path ***tail,
 				mode_i = tp[i].entry.mode;
 			}
 			else {
-				oid_i = null_oid();
+				oid_i = null_oid(the_hash_algo);
 				mode_i = 0;
 			}
 
diff --git a/upload-pack.c b/upload-pack.c
index 67063708b8..02ce633602 100644
--- a/upload-pack.c
+++ b/upload-pack.c
@@ -1449,7 +1449,7 @@ void upload_pack(const int advertise_refs, const int stateless_rpc,
 		for_each_namespaced_ref_1(send_ref, &data);
 		if (!data.sent_capabilities) {
 			const char *refname = "capabilities^{}";
-			write_v0_ref(&data, refname, refname, null_oid());
+			write_v0_ref(&data, refname, refname, null_oid(the_hash_algo));
 		}
 		/*
 		 * fflush stdout before calling advertise_shallow_grafts because send_ref
diff --git a/wt-status.c b/wt-status.c
index 1da5732f57..454601afa1 100644
--- a/wt-status.c
+++ b/wt-status.c
@@ -1824,10 +1824,10 @@ void wt_status_get_state(struct repository *r,
 	if (!sequencer_get_last_command(r, &action)) {
 		if (action == REPLAY_PICK && !state->cherry_pick_in_progress) {
 			state->cherry_pick_in_progress = 1;
-			oidcpy(&state->cherry_pick_head_oid, null_oid());
+			oidcpy(&state->cherry_pick_head_oid, null_oid(the_hash_algo));
 		} else if (action == REPLAY_REVERT && !state->revert_in_progress) {
 			state->revert_in_progress = 1;
-			oidcpy(&state->revert_head_oid, null_oid());
+			oidcpy(&state->revert_head_oid, null_oid(the_hash_algo));
 		}
 	}
 	if (get_detached_from)
diff --git a/xdiff-interface.c b/xdiff-interface.c
index 3bd61f26e9..77712811ff 100644
--- a/xdiff-interface.c
+++ b/xdiff-interface.c
@@ -181,7 +181,7 @@ void read_mmblob(mmfile_t *ptr, const struct object_id *oid)
 	unsigned long size;
 	enum object_type type;
 
-	if (oideq(oid, null_oid())) {
+	if (oideq(oid, null_oid(the_hash_algo))) {
 		ptr->ptr = xstrdup("");
 		ptr->size = 0;
 		return;