fix(core): return null when getDirectiveMetadata is called with null or undefined

Safely return null instead of throwing an unhandled TypeError when getDirectiveMetadata is called with a falsy directive or component instance.

(cherry picked from commit cea6896a0f)

packages/core/src/render3/util/discovery_utils.ts

@@ -304,6 +304,9 @@ export type DirectiveDebugMetadata =
 export function getDirectiveMetadata(
   directiveOrComponentInstance: any,
 ): AngularComponentDebugMetadata | AngularDirectiveDebugMetadata | null {
+  if (!directiveOrComponentInstance) {
+    return null;
+  }
   const {constructor} = directiveOrComponentInstance;
   if (!constructor) {
     throw new Error('Unable to find the instance constructor');

packages/core/test/acceptance/discover_utils_spec.ts

@@ -405,6 +405,11 @@ describe('discovery utils', () => {
       expect(metadata!.inputs).toEqual({a: 'b'});
       expect(metadata!.outputs).toEqual({c: 'd'});
     });
+
+    it('should return null when passed null or undefined', () => {
+      expect(getDirectiveMetadata(null)).toBeNull();
+      expect(getDirectiveMetadata(undefined)).toBeNull();
+    });
   });
 });