docstr: Test _proto_to_dict() to deserialize protobuf with empty fields
code: def test_empty_fields(self):
      """Test _proto_to_dict() to deserialize protobuf with empty fields"""
      proto = DeploymentConfigProto()
      result = _proto_to_dict(proto)
  
      # Defaults are filled.
      assert result["num_replicas"] == 0
      assert result["max_concurrent_queries"] == 0
      assert result["user_config"] == b""
      assert result["user_configured_option_names"] == []
  
      # Nested profobufs don't exist.
      assert "autoscaling_config" not in result
  
imports: import pytest
  from ray import cloudpickle
  from ray._private.pydantic_compat import ValidationError
  from ray._private.utils import import_attr
  from ray.serve._private.config import DeploymentConfig, ReplicaConfig, _proto_to_dict
  from ray.serve._private.constants import DEFAULT_AUTOSCALING_POLICY, DEFAULT_GRPC_PORT
  from ray.serve._private.utils import DEFAULT
  from ray.serve.autoscaling_policy import default_autoscaling_policy
  from ray.serve.config import AutoscalingConfig, DeploymentMode, HTTPOptions, ProxyLocation, gRPCOptions
  from ray.serve.generated.serve_pb2 import AutoscalingConfig
  from ray.serve.generated.serve_pb2 import DeploymentConfig
  from ray.serve.generated.serve_pb2 import DeploymentLanguage
  from ray.serve.generated.serve_pb2_grpc import add_UserDefinedServiceServicer_to_server
  from ray.serve.schema import DeploymentSchema, HTTPOptionsSchema, ServeApplicationSchema, ServeDeploySchema
label_desc: Use image node_id 1 for calling the TestProtoToDict obj's underlying member method code with example usage: obj.test_empty_fields() without return types