def add_dict_to_hash(a_hash, a_dict):
    """Adds `a_dict` to `a_hash`

    Args:
       a_hash (`Hash`): the secure hash, e.g created by hashlib.md5
       a_dict (dict[string, [string]]): the dictionary to add to the hash

    """
    if a_dict is None:
        return
    for k, v in a_dict.items():
        a_hash.update(b'\x00' + k.encode('utf-8') + b'\x00' + v.encode('utf-8'))