What causes "Parameter name cannot be empty" in apache/beam?

Fix the source dict/config so every key is a non-empty parameter name.

apache/beam · error · ValueError

Parameter name cannot be empty

Error message

Parameter name cannot be empty

What it means

When building a cross-language (Java) transform via SchemaTransform, each keyword argument to build() becomes a named schema field. Beam raises this ValueError if a keyword argument's name is empty, because a schema field cannot have an empty identifier.

Solutions

Fix the source dict/config so every key is a non-empty parameter name.
Filter out empty keys before calling build().
Check for typos or failed string interpolation producing '' as a key.

Example fix

# before
builder.build(**{name: value for name, value in params.items() if name in keep})  # '' slips through
# after
builder.build(**{name: value for name, value in params.items() if name and name in keep})

Defensive patterns

Strategy: validation

Validate before calling

bad = [k for k in kwargs if not k]
if bad:
    raise ValueError('empty parameter names: %r' % bad)
builder.build(**kwargs)

Type guard

def valid_kwargs(kwargs) -> bool:
    return all(isinstance(k, str) and k for k in kwargs)

Try / catch

try:
    builder.build(**kwargs)
except ValueError as e:
    if 'Parameter name cannot be empty' in str(e):
        kwargs = {k: v for k, v in kwargs.items() if k}
        builder.build(**kwargs)
    else:
        raise

Prevention

Validate dynamically built kwargs keys before build().
Never spread dicts with possibly-empty keys via **.
Log the kwargs dict when building transforms programmatically.

When it happens

Trigger: Calling builder.build(**kwargs) where one of the kwargs keys is an empty string, typically via **{'': value} or dynamically constructed parameter names.

Common situations: Programmatically building kwargs from config dictionaries or parsed identifiers where a key was dropped or defaulted to empty string.

Understand the failure class

Background: "must not be empty", "cannot be empty" — required-field validation errors across open-source libraries — this error's family across 41 libraries.

Related errors

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/b3b028c4f65ff3a7. Report an issue: GitHub.

Appendix: source

Thrown at sdks/python/apache_beam/transforms/external.py:146

    :return: ExternalConfigurationPayload
    """
    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):
  """

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