Follow up fix for merging errors from batch BigQuery inserts (#1348). (#1350)

* Follow up fix for merging errors from batch BigQuery inserts (#1348).

* fix pylint false positive

Author: Dor1s

src/python/google_cloud_utils/big_query.py

@@ -370,7 +370,7 @@ def insert(self, inserts):
       A json explained here:
       https://cloud.google.com/bigquery/docs/reference/rest/v2/tabledata/insertAll
     """
-    result = None
+    result = {}
     for i in range(0, len(inserts), INSERT_BATCH_SIZE):
       response = self._insert_batch(
           inserts[i:min(len(inserts), i + INSERT_BATCH_SIZE)])
@@ -379,8 +379,18 @@ def insert(self, inserts):
       time.sleep(1)
 
       if not result:
+        # Use result from the first batch, appending errors from the rest.
         result = response
       else:
-        result['insertErrors'].extend(response['insertErrors'])
+        # If there are new errors from the current batch, append to the result.
+        new_errors = response.get('insertErrors')
+        if not new_errors:
+          continue
+
+        # Apparently result may not have errors, be careful.
+        if result.get('insertErrors'):
+          result['insertErrors'].extend(new_errors)
+        else:
+          result['insertErrors'] = new_errors
 
     return result