@staticmethod
def __add_optional_fields(dict_to_add, **kwargs):
    """
        Add optional field to dict
        Additional field(s) will be preceded with underscore in front of the field name

        :param dict_to_add: Dict to be added with optional field(s)
        :param kwargs: Optional field(s)
        :return: Dict with optional field(s)
        """
    for key, value in kwargs.items():
        key = '_' + str(key)
        dict_to_add[key] = value
    return dict_to_add
