Fix bug where backdrop calls method on null if it is already removed from the body (#34014)

Co-authored-by: Rohit Sharma <rohit2sharma95@gmail.com>

js/src/util/backdrop.js

@@ -116,7 +116,11 @@ class Backdrop {
 
     EventHandler.off(this._element, EVENT_MOUSEDOWN)
 
-    this._getElement().parentNode.removeChild(this._element)
+    const { parentNode } = this._getElement()
+    if (parentNode) {
+      parentNode.removeChild(this._element)
+    }
+
     this._isAppended = false
   }
 

js/tests/unit/util/backdrop.spec.js

@@ -129,6 +129,25 @@ describe('Backdrop', () => {
     })
   })
 
+  it('should not error if the backdrop no longer has a parent', done => {
+    const instance = new Backdrop({
+      isVisible: true,
+      isAnimated: true
+    })
+    const getElements = () => document.querySelectorAll(CLASS_BACKDROP)
+
+    instance.show(() => {
+      instance.hide(() => {
+        expect(getElements().length).toEqual(0)
+
+        // replace the fixture, which was just wiped out
+        fixtureEl = getFixture()
+        done()
+      })
+      document.body.innerHTML = 'changed'
+    })
+  })
+
   describe('click callback', () => {
     it('it should execute callback on click', done => {
       const spy = jasmine.createSpy('spy')