JSONDecodeError when getting results via IonQ Backend if not measuring all qubits

Sharing on behalf of @amirebrahimi:

I'm getting an error when calling job.result() from ionq.simulator. Details in thread.

---------------------------------------------------------------------------
JSONDecodeError                           Traceback (most recent call last)
/tmp/ipykernel_15433/1564545644.py in <module>
      1 # print(result)
----> 2 print(job.result())

/usr/local/lib/python3.7/site-packages/azure/quantum/qiskit/job.py in result(self, timeout)
     75 
     76         success = self._azure_job.details.status == "Succeeded"
---> 77         results = self._format_results()
     78 
     79         return Result.from_dict(

/usr/local/lib/python3.7/site-packages/azure/quantum/qiskit/job.py in _format_results(self)
    118 
    119             elif (self._azure_job.details.output_data_format == IONQ_OUTPUT_DATA_FORMAT):
--> 120                 job_result["data"] = self._format_ionq_results()
    121                 job_result["header"] = self._azure_job.details.metadata
    122 

/usr/local/lib/python3.7/site-packages/azure/quantum/qiskit/job.py in _format_ionq_results(self)
    140         if "meas_map" not in self._azure_job.details.metadata or "num_qubits" not in self._azure_job.details.metadata:
    141             raise ValueError(f"Job with ID {self.id()} does not have the required metadata to format IonQ results.")
--> 142         meas_map = json.loads(self._azure_job.details.metadata.get("meas_map"))
    143         num_qubits = self._azure_job.details.metadata.get("num_qubits")
    144 

/usr/local/lib/python3.7/json/__init__.py in loads(s, encoding, cls, object_hook, parse_float, parse_int, parse_constant, object_pairs_hook, **kw)
    346             parse_int is None and parse_float is None and
    347             parse_constant is None and object_pairs_hook is None and not kw):
--> 348         return _default_decoder.decode(s)
    349     if cls is None:
    350         cls = JSONDecoder

/usr/local/lib/python3.7/json/decoder.py in decode(self, s, _w)
    335 
    336         """
--> 337         obj, end = self.raw_decode(s, idx=_w(s, 0).end())
    338         end = _w(s, end).end()
    339         if end != len(s):

/usr/local/lib/python3.7/json/decoder.py in raw_decode(self, s, idx)
    353             obj, end = self.scan_once(s, idx)
    354         except StopIteration as err:
--> 355             raise JSONDecodeError("Expecting value", s, err.value) from None
    356         return obj, end

JSONDecodeError: Expecting value: line 1 column 14 (char 13)

A temporary fix: measure all your qubits
The problem is that meas_map may have None for any qubits you don't measure. which is breaking the parsing

Start in azure/quantum/qiskit/job.py, especially _format_results and _format_ionq_results, and reproduce the failure with an IonQ job that does not measure every qubit. Check how meas_map is handled before JSON parsing. Done means job.result() formats results without JSONDecodeError for partially measured circuits.