Generic is_missing function that handles NaN and NaT.

def is_missing(data, missing_value):
    """
    Generic is_missing function that handles NaN and NaT.
    """
    if is_float(data) and isnan(missing_value):
        return isnan(data)
    elif is_datetime(data) and isnat(missing_value):
        return isnat(data)
    return (data == missing_value)