import re


def validate_email(value):
    """Validates email address value.

    :param value: A candidate value for an email address
    :type value: string | NoneType
    :return: True if values is a valid email address or None. Otherwise returns False
    :rtype bool
    """
    return value is None or bool(re.match(r'[^@]+@[^@]+\.[^@]+', value))