fix batching bug in diff query (#6483)

* fix batching bug in diff query

* add changelog

Author: ajtmccarty

backend/infrahub/core/diff/query_parser.py

@@ -526,7 +526,11 @@ def get_current_node_field_specifiers(self) -> NodeFieldSpecifierMap:
         return self._current_node_field_specifiers
 
     def read_result(self, query_result: QueryResult) -> None:
-        path = query_result.get_path(label="diff_path")
+        try:
+            path = query_result.get_path(label="diff_path")
+        except ValueError:
+            # the path was null, so nothing to read
+            return
         database_path = DatabasePath.from_cypher_path(cypher_path=path)
         self._parse_path(database_path=database_path)
         self._current_node_field_specifiers = None

backend/infrahub/core/query/diff.py

@@ -201,6 +201,13 @@ def __init__(
     diff_rel_paths = [], item IN [penultimate_path, peer_path] |
     CASE WHEN item IS NULL THEN diff_rel_paths ELSE diff_rel_paths + [item] END
 ) AS diff_rel_paths, has_more_data
+// ------------------------
+// make sure we still include has_more_data if diff_rel_paths is empty
+// ------------------------
+WITH CASE
+    WHEN diff_rel_paths = [] THEN [NULL]
+    ELSE diff_rel_paths
+END AS diff_rel_paths, has_more_data
     """
 
     def get_previous_base_path_query(self, db: InfrahubDatabase) -> str:

changelog/+diff_batch_bug.fixed.md

@@ -0,0 +1 @@
+Fix a problem in the logic to calculate a diff that could cause it to quit too early under certain unlikely circumstances