[0.5] Treat undefined selection the same as null in $generateNodesFro…

…mHtml (facebook#2948)

* Treat undefined selection the same as null in $generateNodesFromHtml

* fix mistake

* address feedback

* reorder params and remove undefined check

packages/lexical-html/src/index.ts

@@ -68,19 +68,17 @@ export function $generateHtmlFromNodes(
 
   for (let i = 0; i < topLevelChildren.length; i++) {
     const topLevelNode = topLevelChildren[i];
-    if (selection !== undefined) {
-      $appendNodesToHTML(editor, selection, topLevelNode, container);
-    }
+    $appendNodesToHTML(editor, topLevelNode, container, selection);
   }
 
   return container.innerHTML;
 }
 
 function $appendNodesToHTML(
   editor: LexicalEditor,
-  selection: RangeSelection | NodeSelection | GridSelection | null,
   currentNode: LexicalNode,
   parentElement: HTMLElement | DocumentFragment,
+  selection: RangeSelection | NodeSelection | GridSelection | null = null,
 ): boolean {
   let shouldInclude = selection != null ? currentNode.isSelected() : true;
   const shouldExclude =
@@ -108,9 +106,9 @@ function $appendNodesToHTML(
     const childNode = children[i];
     const shouldIncludeChild = $appendNodesToHTML(
       editor,
-      selection,
       childNode,
       fragment,
+      selection,
     );
 
     if (