fix(gatsby-source-drupal): Verify nodes exist before looping through them (#22898)

* Verify nodes exist before looping through them

* Update to push nodes directly inside loop

Co-Authored-By: Peter van der Zee <209817+pvdz@users.noreply.github.com>

Co-authored-by: Peter van der Zee <209817+pvdz@users.noreply.github.com>

Author: smthomas

packages/gatsby-source-drupal/src/utils.js

@@ -147,10 +147,10 @@ const handleWebhookUpdate = async (
     nodesToUpdate.push(...addedReferencedNodes)
   } else {
     // if we are inserting new node, we need to update all referenced nodes
-    const newNodeReferencedNodes = referencedNodesLookup
-      .get(newNode)
-      .map(id => getNode(id))
-    nodesToUpdate.push(...newNodeReferencedNodes)
+    const newNodes = referencedNodesLookup.get(newNode)
+    if (typeof newNodes !== `undefined`) {
+      newNodes.forEach(id => nodesToUpdate.push(getNode(id)))
+    }
   }
 
   // download file