apache/beam · error · ValueError

Received value None for key

Error message

Received value None for key %s. None values are currently not supported

What it means

SchemaTransform builder fields map Python values to schema-typed fields, and Beam does not know how to represent None as a typed field value in this path. Passing None as any keyword value to build() raises this ValueError with the offending key name.

Solutions

Omit None-valued keys entirely instead of passing them (fields default when absent).
Substitute explicit non-None defaults (e.g. '' , 0) when the schema expects a value.
Filter kwargs: build(**{k: v for k, v in kwargs.items() if v is not None}).

Example fix

# before
builder.build(path=input_path, batch_size=None)
# after
builder.build(path=input_path)  # omit None fields; set defaults explicitly if required

Defensive patterns

Strategy: validation

Validate before calling

nones = [k for k, v in kwargs.items() if v is None]
if nones:
    raise ValueError('None values not supported for: %r' % nones)
builder.build(**kwargs)

Type guard

def no_none_values(kwargs) -> bool:
    return all(v is not None for v in kwargs.values())

Try / catch

try:
    builder.build(**kwargs)
except ValueError as e:
    if 'None values are currently not supported' in str(e):
        builder.build(**{k: v for k, v in kwargs.items() if v is not None})
    else:
        raise

Prevention

Filter None values out of config dicts before build().
Give optional settings concrete defaults instead of None.
Keep optional schema fields absent rather than None.

When it happens

Trigger: Calling builder.build(field=None) or passing a dict with None values via **kwargs to a SchemaTransform provider's build().

Common situations: Config-driven pipelines where optional settings are None by default, or merging partial configurations into kwargs.

Related errors

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/470bac02bb06e5c9. Report an issue: GitHub.

Appendix: source

Thrown at sdks/python/apache_beam/transforms/external.py:148

    raise NotImplementedError

  def payload(self):
    """
    The serialized ExternalConfigurationPayload

    :return: bytes
    """
    return self.build().SerializeToString()

  def _get_schema_proto_and_payload(self, **kwargs):
    named_fields = []
    fields_to_values = OrderedDict()

    for key, value in kwargs.items():
      if not key:
        raise ValueError('Parameter name cannot be empty')
      if value is None:
        raise ValueError(
            'Received value None for key %s. None values are currently not '
            'supported' % key)
      named_fields.append(
          (key, convert_to_typing_type(instance_to_type(value))))
      fields_to_values[key] = value

    schema_proto = named_fields_to_schema(named_fields)
    row = named_tuple_from_schema(schema_proto)(**fields_to_values)
    schema = named_tuple_to_schema(type(row))

    payload = RowCoder(schema).encode(row)
    return (schema_proto, payload)


class SchemaBasedPayloadBuilder(PayloadBuilder):
  """
  Base class for building payloads based on a schema that provides
  type information for each configuration value to encode.

View on GitHub (pinned to 12126d8942)