[Runtime] Accept Nil in the patched bundleForClass:.

The patched +[NSBundle bundleForClass:] crashes on Nil, while the original Foundation implementation returns the main bundle. Avoid the crash and pass Nil through to Foundation. This also ensures that Nil is passed through to class_getImageName rather than crashing.

SR-9188 rdar://problem/45849924

stdlib/public/runtime/ObjCRuntimeGetImageNameFromClass.mm

@@ -56,8 +56,11 @@ static objc_hook_getImageName defaultGetImageNameFromClass = nullptr;
 /// Get the image name corresponding to a Swift class, accounting for
 /// dynamically-initialized class metadata. Returns NO for ObjC classes.
 static BOOL
-getImageNameFromSwiftClass(Class _Nonnull objcClass,
+getImageNameFromSwiftClass(Class _Nullable objcClass,
                            const char * _Nullable * _Nonnull outImageName) {
+  if (objcClass == Nil)
+    return NO;
+  
   auto *classAsMetadata = reinterpret_cast<const ClassMetadata *>(objcClass);
 
   // Is this a Swift class?

test/stdlib/Bundle.swift

@@ -0,0 +1,25 @@
+// RUN: %target-run-simple-swift
+// REQUIRES: executable_test
+// REQUIRES: objc_interop
+
+import Foundation
+import StdlibUnittest
+
+var BundleTests = TestSuite("BundleTests")
+
+BundleTests.test("Bundle.bundleForNilClass") {
+  // Ensure that bundleForClass: tolerates a nil parameter. The
+  // Foundation implementation does. The patched version from
+  // ObjCRuntimeGetImageNameFromClass did not.
+  //
+  // SR-9188
+  typealias BundleForClassFunc =
+    @convention(c) (AnyObject, Selector, AnyObject?) -> Bundle
+  
+  let sel = #selector(Bundle.init(for:))
+  let imp = unsafeBitCast(Bundle.method(for: sel), to: BundleForClassFunc.self)
+  let bundleForNil = imp(Bundle.self, sel, nil);
+  expectEqual(Bundle.main, bundleForNil)
+}
+
+runAllTests()