def ninja_key_value_pairs(key, values):
    """Add include/subninja fields
    Args:
        key (str): such as "include", "subninja"
        values (list): a list of strings
    Returns:
        a string
    """
    if isinstance(values, list):
        return '\n\n'.join(map(lambda x: '{} {}'.format(key, x), values))
    else:
        return '{} {}'.format(key, values)
