code: def testMakeProtoPlaceholder_NoneExecPropIntoOptionalField(self):
      # When an exec prop has type Union[T, None] and the user passes None, it is
      # actually completely absent from the exec_properties dict in
      # ExecutionInvocation.
      actual = resolve(
          _UpdateOptions(
              reload_policy=ph.exec_property("reload_policy")
          ),
          exec_properties={},  # Intentionally empty.
      )
      self.assertProtoEquals(
          "",
          parse_text_proto(actual, pipeline_pb2.UpdateOptions),
      )
  
imports: import base64
  import functools
  from typing import Any, Dict, Optional, Type, TypeVar
  import tensorflow
  from tfx.dsl.compiler import placeholder_utils
  from tfx.dsl.placeholder import placeholder
  from tfx.dsl.placeholder import proto_placeholder
  from tfx.orchestration.portable import data_types
  from tfx.proto.orchestration import execution_invocation_pb2
  from tfx.proto.orchestration import pipeline_pb2
  from google.protobuf import message
  from google.protobuf import text_format
  from ml_metadata.proto import metadata_store_pb2
label_desc: Use image node_id 12 for calling the ProtoPlaceholderTest obj's underlying member method code with example usage: obj.testMakeProtoPlaceholder_NoneExecPropIntoOptionalField() without return types