def fields_values(d, k):
    """
    >>> data = {'name1': ['value1.1', 'value1.2'], 'name2': ['value2.1', 'value2.2'], }
    >>> print(fields_values(data, 'name1'))
    value1.1,value1.2
    """
    values = d.get(k, [])
    return ",".join(map(str, values))