fix problems w meta and dataframe

document_stores/elasticsearch/src/elasticsearch_haystack/document_store.py

@@ -221,7 +221,7 @@ def _deserialize_document(self, hit: Dict[str, Any]) -> Document:
             dataframe=data["dataframe"],
             blob=data["blob"],
             mime_type=data["mime_type"],
-            meta=data["meta"],
+            meta=data.get("meta", {}),
             score=data["score"],
             embedding=data["embedding"],
         )
@@ -237,9 +237,6 @@ def _serialize_document(self, doc: Document) -> Dict[str, Any]:
         # Otherwise we'd have to filter out the fields that are not part of the
         # Document dataclass and keep them as metadata. This is faster and easier.
         res = {**doc.to_dict(), **doc.meta}
-        if res["dataframe"] is not None:
-            # Convert dataframe to a json string
-            res["dataframe"] = res["dataframe"].to_json()
         # if res["embedding"] is not None:
         #     res["embedding"] = res["embedding"].tolist()
         return res