Initialize a Expansions object from a json dictionary.

def _from_dict(cls, _dict):
        """Initialize a Expansions object from a json dictionary."""
        args = {}
        if 'expansions' in _dict:
            args['expansions'] = [
                Expansion._from_dict(x) for x in (_dict.get('expansions'))
            ]
        else:
            raise ValueError(
                'Required property \'expansions\' not present in Expansions JSON'
            )
        return cls(**args)