Update image-preview.test.js

Author: gabrieldagama

dev/tests/js/jasmine/tests/app/code/Magento/Ui/base/js/grid/columns/image-preview.test.js

@@ -62,7 +62,7 @@ define([
                 expect(imagePreview.lastOpenedImage()).toBe(record._rowIndex);
 
                 imagePreview.hide();
-                expect(imagePreview.lastOpenedImage()).toBe(false);
+                expect(imagePreview.lastOpenedImage()).toBe(null);
             });
 
         });