Only check MediaPlaceholder allowedTypes array length if prop exists (#…

…11694)

* Only check MediaPlaceholder allowedTypes array length if allowedTypes prop exists

Fixes #11692

Adds basic unit test to demonstrate the bug described in #11692.

* Initialize allowedTypes to [] instead of modifying conditional

* Reinstate array length check

packages/editor/src/components/media-placeholder/index.js

@@ -131,7 +131,7 @@ class MediaPlaceholder extends Component {
 			onHTMLDrop = noop,
 			multiple = false,
 			notices,
-			allowedTypes,
+			allowedTypes = [],
 		} = this.props;
 
 		const {

packages/editor/src/components/media-placeholder/test/index.js

@@ -0,0 +1,17 @@
+/**
+ * External dependencies
+ */
+import { mount } from 'enzyme';
+
+/**
+ * Internal dependencies
+ */
+import MediaPlaceholder from '../';
+
+describe( 'MediaPlaceholder', () => {
+	it( 'renders successfully when allowedTypes property is not specified', () => {
+		expect( () => mount(
+			<MediaPlaceholder />
+		) ).not.toThrow();
+	} );
+} );