'Return the attribute from the json data and instantiate the class.
:param dict data: dictionary used to put together the model or None
:param str attribute: key of the attribute
:param class cl: class that will be instantiated
:returns: instantiated class or None
:rtype: object or None'

@classmethod
def _class_attribute(cls, data, attribute, cl, *args, **kwargs):

    value = cls._get_attribute(data, attribute)
    if value:
        return cl(value, *args, **kwargs)
    return value
