diff --git a/aiola/clients/stt/client.py b/aiola/clients/stt/client.py
index a88c978..59cd37e 100644
--- a/aiola/clients/stt/client.py
+++ b/aiola/clients/stt/client.py
@@ -34,7 +34,9 @@ def __init__(self, options: AiolaClientOptions, auth: AuthClient | AsyncAuthClie
     def _build_url(self, query_params: dict[str, str]) -> str:
         """Return base URL with encoded query parameters."""
         try:
-            return f"{self._options.base_url}?{urlencode(query_params)}"
+            # Filter out None values from query parameters
+            filtered_params = {k: v for k, v in query_params.items() if v is not None}
+            return f"{self._options.base_url}?{urlencode(filtered_params)}"
         except Exception as exc:
             raise AiolaError("Failed to build streaming URL") from exc
 
@@ -66,7 +68,7 @@ def _build_query_and_headers(
             "lang_code": lang_code or "en",
             "time_zone": time_zone or "UTC",
             "keywords": json.dumps(keywords or {}),
-            "tasks_config": json.dumps(tasks_config or {}),
+            "tasks_config": json.dumps(tasks_config) if tasks_config is not None else None,
             "x-aiola-api-token": access_token,
         }
 
diff --git a/tests/unit/stt/test_stt_client.py b/tests/unit/stt/test_stt_client.py
index 8780cbc..96c2687 100644
--- a/tests/unit/stt/test_stt_client.py
+++ b/tests/unit/stt/test_stt_client.py
@@ -341,15 +341,14 @@ def test_stt_stream_with_no_tasks_config(patch_dummy_socket):
     # Access the underlying socket to validate connection parameters
     sio = connection._sio
 
-    # Verify None tasks_config is serialized as empty JSON object
+    # Verify None tasks_config is excluded from URL parameters
     kwargs = sio.connect_kwargs
     url = kwargs["url"]
     parsed = urllib.parse.urlparse(url)
     query = urllib.parse.parse_qs(parsed.query)
 
-    tasks_config_json = query["tasks_config"][0]
-    parsed_tasks_config = json.loads(tasks_config_json)
-    assert parsed_tasks_config == {}
+    # tasks_config should not be present in query parameters when None
+    assert "tasks_config" not in query
 
 
 def test_stt_stream_with_all_tasks_config(patch_dummy_socket):