Fix serializer for empty string extra connection

airflow-core/src/airflow/api_fastapi/core_api/datamodels/connections.py

@@ -53,16 +53,16 @@ def redact_password(cls, v: str | None, field_info: ValidationInfo) -> str | Non
     @field_validator("extra", mode="before")
     @classmethod
     def redact_extra(cls, v: str | None) -> str | None:
-        if v is None:
-            return None
+        if v is None or v == "":
+            return v
         try:
             extra_dict = json.loads(v)
             redacted_dict = redact(extra_dict)
             return json.dumps(redacted_dict)
         except json.JSONDecodeError:
             # Do not return un-redacted extra because this could cause sensitive information to be exposed.
-            # This code path should never been hit as ``Connection._validate_extra`` sure that ``extra`` is
-            # always a valid JSON string. We add this safeguard just in case and to make the coupling
+            # This code path should never be hit as ``Connection._validate_extra`` makes sure that ``extra`` is
+            # always a valid JSON string (if truthy). We add this safeguard just in case and to make the coupling
             # explicit.
             raise ValueError(
                 "This code path should never happen as persisted Connections (DB layer) should always enforce `extra` as a JSON string."

airflow-core/tests/unit/api_fastapi/core_api/routes/public/test_connections.py

@@ -168,6 +168,19 @@ def test_get_should_respond_200_with_extra(self, test_client, session):
         assert body["conn_type"] == TEST_CONN_TYPE
         assert body["extra"] == '{"extra_key": "extra_value"}'
 
+    @pytest.mark.parametrize("extra_value", [None, ""])
+    def test_get_should_respond_200_with_empty_extra(self, test_client, session, extra_value):
+        """Empty string or NULL extra should not break serialization (regression test for #64950)."""
+        self.create_connection()
+        connection = session.scalars(select(Connection)).first()
+        connection.extra = extra_value
+        session.commit()
+        response = test_client.get(f"/connections/{TEST_CONN_ID}")
+        assert response.status_code == 200
+        body = response.json()
+        assert body["connection_id"] == TEST_CONN_ID
+        assert body["extra"] == extra_value
+
     @pytest.mark.enable_redact
     def test_get_should_respond_200_with_extra_redacted(self, test_client, session):
         self.create_connection()