Set default factory for optional dictionary fields in GenerateUrlRequ…

…est parameter

mediaflow_proxy/schemas.py

@@ -7,9 +7,11 @@ class GenerateUrlRequest(BaseModel):
     mediaflow_proxy_url: str = Field(..., description="The base URL for the mediaflow proxy.")
     endpoint: str | None = Field(None, description="The specific endpoint to be appended to the base URL.")
     destination_url: str | None = Field(None, description="The destination URL to which the request will be proxied.")
-    query_params: dict | None = Field(None, description="Query parameters to be included in the request.")
-    request_headers: dict | None = Field(None, description="Headers to be included in the request.")
-    response_headers: dict | None = Field(None, description="Headers to be included in the response.")
+    query_params: dict | None = Field(
+        default_factory=dict, description="Query parameters to be included in the request."
+    )
+    request_headers: dict | None = Field(default_factory=dict, description="Headers to be included in the request.")
+    response_headers: dict | None = Field(default_factory=dict, description="Headers to be included in the response.")
     expiration: int | None = Field(
         None, description="Expiration time for the URL in seconds. If not provided, the URL will not expire."
     )