Merge branch 'dev' into memgraph-integration-fixes

cognee/infrastructure/databases/graph/memgraph/memgraph_adapter.py

@@ -376,12 +376,19 @@ class MemgraphAdapter(GraphDBInterface):
 
             The result of the edge addition operation, including relationship details.
         """
+
+        exists = await asyncio.gather(self.has_node(str(from_node)), self.has_node(str(to_node)))
+
+        if not all(exists):
+            return None
+
         serialized_properties = self.serialize_properties(edge_properties or {})
 
         query = dedent(
             f"""\
             MATCH (from_node {{id: $from_node}}),
                   (to_node {{id: $to_node}})
+            WHERE from_node IS NOT NULL AND to_node IS NOT NULL
             MERGE (from_node)-[r:{relationship_name}]->(to_node)
             ON CREATE SET r += $properties, r.updated_at = timestamp()
             ON MATCH SET r += $properties, r.updated_at = timestamp()