Added null checks

scripts/Utils/swapElements.ts

@@ -1,22 +1,23 @@
+// swapElements assumes that both elements have valid parent nodes.
 export function swapElements(a: Node, b: Node) {
-	let parent = b.parentNode
+	let bParent = b.parentNode as Node
 	let bNext = b.nextSibling
 
 	// Special case for when a is the next sibling of b
 	if(bNext === a) {
 		// Just put a before b
-		parent.insertBefore(a, b)
+		bParent.insertBefore(a, b)
 	} else {
 		// Insert b right before a
-		a.parentNode.insertBefore(b, a)
+		(a.parentNode as Node).insertBefore(b, a)
 
 		// Now insert a where b was
 		if(bNext) {
 			// If there was an element after b, then insert a right before that
-			parent.insertBefore(a, bNext)
+			bParent.insertBefore(a, bNext)
 		} else {
 			// Otherwise just append it as the last child
-			parent.appendChild(a)
+			bParent.appendChild(a)
 		}
 	}
 }