improve readability

Author: aMahanna

arango/collection.py

@@ -189,7 +189,7 @@ def _ensure_key_in_body(self, body: Json, index: Optional[int] = None) -> Json:
             body = body.copy()
             body["_key"] = doc_id[len(self._id_prefix) :]
             return body
-        elif index:
+        elif index is not None:
             body = body.copy()
             body["_key"] = str(index)
             return body