<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def json_ld(self, output, **kwargs):
 """ Returns the json-ld formated result """

        raw_json_ld = output.serialize(format='json-ld',
                                       context=self.context).decode()
        # if there are fields that should be returned as arrays convert all
        # non-array fields to an array
        if not self.array_fields:
            return raw_json_ld
        json_data = json.loads(raw_json_ld)
        for i, item in enumerate(json_data['@graph']):
            if item.get("@type") in self.array_fields:
                test_flds = self.array_fields[item['@type']]
                for key, val in item.items():
                    if key in test_flds and not isinstance(val, list):
                        json_data['@graph'][i][key] = [val]
        # print(json.dumps(json_data, indent=4))
        return json.dumps(json_data, indent=4)