fix: 🐛 Check merge key for merge data source (#3901)

extensions/default/src/MergeDataSource/index.ts

@@ -60,7 +60,14 @@ export const callForAllDataSourcesAsync = async ({
 
   await Promise.allSettled(promises);
 
-  return uniqBy(mergedData.flat(), obj => obj[mergeKey]);
+  let results = [];
+  if (mergeKey) {
+    results = uniqBy(mergedData.flat(), obj => get(obj, mergeKey));
+  } else {
+    results = mergedData.flat();
+  }
+
+  return results;
 };
 
 /**