code: def testMakeProtoPlaceholder_RejectsMapFieldScalarNoneKey(self):
      with self.assertRaises(ValueError):
          resolve(
              _ExecutionInvocation(
                  extra_flags=[
                      (
                          ph.exec_property(
                              "reload_policy"
                          ),  # Will be None.
                          "foo",
                      )
                  ]
              ),
              exec_properties={},  # Intentionally empty.
          )
      with self.assertRaises(ValueError):
          resolve(_ExecutionInvocation(extra_flags={None: "foo"}))
  
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 35 for calling the ProtoPlaceholderTest obj's underlying member method code with example usage: obj.testMakeProtoPlaceholder_RejectsMapFieldScalarNoneKey() without return types