from typing import Optional
import re


def _normalize(x: Optional[str]) -> Optional[str]:
    """
    Normalize string to lowercase, no whitespace, and no underscores.

    Examples
    --------
    >>> _normalize('Offshore Wind')
    'offshorewind'
    >>> _normalize('OffshoreWind')
    'offshorewind'
    >>> _normalize('Offshore_Wind')
    'offshorewind'
    >>> _normalize(None) is None
    True
    """
    if not x:
        return x
    return re.sub(r"\s+|_", "", x.lower())