code: def verify_formatter(
      formatter: typing.Optional[str], *, required: bool = REQUIRED
  ) -> None:
      if formatter is None:
          if required:
              raise ValueError("missing formatter")
      elif formatter.lower() not in FORMATTERS:
          raise ValueError(
              f"unknown formatter: {formatter!r}"
              f" (must be None or one of {sorted(FORMATTERS)})"
          )
  
file_path: graphviz/graphviz/parameters/formatters.py
imports: import typing
  from .None import base
label_desc: Use image node_id 1 for calling a global function with example usage: verify_formatter(formatter) without return types