def _has_message_field(message, field_key):
    """
    Returns whether the message has the given field.
    
    
    Parameters
    ----------
    message : ``Message``
        The message to check whether it has the field.
    field_key : `int`
        Message field key to check.
    
    Returns
    -------
    has_field : `bool`
    """
    fields = message._fields
    if (fields is None):
        has_field = False
    else:
        has_field = (field_key in fields)
    
    return has_field