Mark the window object for Window as not required, and guard against missing data

__tests__/src/components/Window.test.js

@@ -7,6 +7,10 @@ import WindowMiddleContent from '../../../src/containers/WindowMiddleContent';
 describe('Window', () => {
   let wrapper;
   const window = { id: 123, xywh: [0, 0, 400, 500] };
+  it('should render nothing, if provided with no window data', () => {
+    wrapper = shallow(<Window />);
+    expect(wrapper.find('.mirador-window')).toHaveLength(0);
+  });
   it('should render outer element', () => {
     wrapper = shallow(<Window window={window} />);
     expect(wrapper.find('.mirador-window')).toHaveLength(1);

src/components/Window.js

@@ -15,6 +15,8 @@ class Window extends Component {
    */
   render() {
     const { manifest, window } = this.props;
+    if (!window) return <></>;
+
     return (
       <div id={window.id} className={ns('window')}>
         <WindowTopBar
@@ -38,11 +40,12 @@ class Window extends Component {
 }
 
 Window.propTypes = {
-  window: PropTypes.object.isRequired, // eslint-disable-line react/forbid-prop-types
+  window: PropTypes.object, // eslint-disable-line react/forbid-prop-types
   manifest: PropTypes.object, // eslint-disable-line react/forbid-prop-types
 };
 
 Window.defaultProps = {
+  window: null,
   manifest: null,
 };