Initialize a CompareReturn object from a json dictionary.

def _from_dict(cls, _dict):
        """Initialize a CompareReturn object from a json dictionary."""
        args = {}
        if 'model_id' in _dict:
            args['model_id'] = _dict.get('model_id')
        if 'model_version' in _dict:
            args['model_version'] = _dict.get('model_version')
        if 'documents' in _dict:
            args['documents'] = [
                Document._from_dict(x) for x in (_dict.get('documents'))
            ]
        if 'aligned_elements' in _dict:
            args['aligned_elements'] = [
                AlignedElement._from_dict(x)
                for x in (_dict.get('aligned_elements'))
            ]
        if 'unaligned_elements' in _dict:
            args['unaligned_elements'] = [
                UnalignedElement._from_dict(x)
                for x in (_dict.get('unaligned_elements'))
            ]
        return cls(**args)