def get_default(value, ctx):
    """
    Get the default argument using a user instance property
    :param value: The name of the property to use
    :param ctx: The click context (which will be used to get the user)
    :return: The default value, or None
    """
    user = ctx.params['user']
    value = getattr(user, value)
    # In our case the empty string means there is no default
    if value == "":
        return None
    return value