Fix new JSONDecodeError

[patudom]

This is a new error for me (and @johnarban) for newly created students when the app is first run.

For example, the app runs for student_id=4153 who already had galaxy measurements.

The following errors are returned if I use create_new_student=True or student_id=4160 whom I just created to test this:

---------------------------------------------------------------------------
JSONDecodeError                           Traceback (most recent call last)
File ~/opt/anaconda3/envs/newbase/lib/python3.8/site-packages/requests/models.py:971, in Response.json(self, **kwargs)
    970 try:
--> 971     return complexjson.loads(self.text, **kwargs)
    972 except JSONDecodeError as e:
    973     # Catch JSON-related errors and raise as requests.JSONDecodeError
    974     # This aliases json.JSONDecodeError and simplejson.JSONDecodeError

File ~/opt/anaconda3/envs/newbase/lib/python3.8/json/__init__.py:357, in loads(s, cls, object_hook, parse_float, parse_int, parse_constant, object_pairs_hook, **kw)
    354 if (cls is None and object_hook is None and
    355         parse_int is None and parse_float is None and
    356         parse_constant is None and object_pairs_hook is None and not kw):
--> 357     return _default_decoder.decode(s)
    358 if cls is None:

File ~/opt/anaconda3/envs/newbase/lib/python3.8/json/decoder.py:337, in JSONDecoder.decode(self, s, _w)
    333 """Return the Python representation of ``s`` (a ``str`` instance
    334 containing a JSON document).
    335 
    336 """
--> 337 obj, end = self.raw_decode(s, idx=_w(s, 0).end())
    338 end = _w(s, end).end()

File ~/opt/anaconda3/envs/newbase/lib/python3.8/json/decoder.py:355, in JSONDecoder.raw_decode(self, 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 1 (char 0)

During handling of the above exception, another exception occurred:

JSONDecodeError                           Traceback (most recent call last)
Cell In[1], line 8
      3 filterwarnings(action="ignore", category=UserWarning)
      5 from cosmicds.app import Application
----> 8 app = Application(story='hubbles_law', update_db=True, show_team_interface=False, allow_advancing=False, create_new_student=True)
      9 # app = Application(story='hubbles_law', update_db=True, show_team_interface=True, allow_advancing=True, student_id=4153) 
     11 app

File ~/Documents/GitHub/cosmicds/cosmicds/app.py:66, in Application.__init__(self, story, *args, **kwargs)
     64     self.observe(lambda x: self._setup(story, **kwargs), 'hub_user_info')
     65 else:
---> 66     self._setup(story, **kwargs)

File ~/Documents/GitHub/cosmicds/cosmicds/app.py:105, in Application._setup(self, story, **kwargs)
    101 # print(f"Student ID: {self.student_id}")
    102 # print(f"Class ID: {self.app_state.classroom['id']}")
    104 self._application_handler = JupyterApplication()
--> 105 self.story_state = story_registry.setup_story(story, self.session,
    106                                               self.app_state)
    108 self._get_student_options()
    110 # Initialize from database

File ~/Documents/GitHub/cosmicds/cosmicds/registries.py:71, in StoryRegistry.setup_story(self, name, session, app_state)
     68     state["stages"] = { int(k) : v for k, v in state["stages"].items() }
     69     story_state.update_from_dict(state)
---> 71 story_state.setup_for_student(app_state)
     73 for k, v in sorted(story_entry['stages'].items()):
     74     stage_cls = v['cls']

File ~/Documents/GitHub/hubbleds/src/hubbleds/story.py:687, in HubblesLaw.setup_for_student(self, app_state)
    685     app_state.update_db = False
    686 self.fetch_student_data()
--> 687 self.fetch_class_data()
    688 self.fetch_example_galaxy_data()

File ~/Documents/GitHub/hubbleds/src/hubbleds/story.py:627, in HubblesLaw.fetch_class_data(self)
    625     timestamp = floor(self.class_last_modified.timestamp() * 1000)
    626     class_data_url = f"{class_data_url}?last_checked={timestamp}"
--> 627 updated_meas, updated_data = self.fetch_measurement_data_and_update(class_data_url, CLASS_DATA_LABEL, prune_none=True, update_if_empty=False, check_update=check_update)
    629 if updated_data is not None:
    630     class_id = self.classroom["id"]

File ~/Documents/GitHub/hubbleds/src/hubbleds/story.py:524, in HubblesLaw.fetch_measurement_data_and_update(self, url, label, prune_none, make_writeable, check_update, update_if_empty, callbacks)
    523 def fetch_measurement_data_and_update(self, url, label, prune_none=False, make_writeable=False, check_update=None, update_if_empty=True, callbacks=None):
--> 524     measurements = self.fetch_measurements(url)
    525     need_update = check_update is None or check_update(measurements)
    526     if not need_update:

File ~/Documents/GitHub/hubbleds/src/hubbleds/story.py:520, in HubblesLaw.fetch_measurements(self, url)
    518 def fetch_measurements(self, url):
    519     response = requests.get(url)
--> 520     res_json = response.json()
    521     return res_json["measurements"]

File ~/opt/anaconda3/envs/newbase/lib/python3.8/site-packages/requests/models.py:975, in Response.json(self, **kwargs)
    971     return complexjson.loads(self.text, **kwargs)
    972 except JSONDecodeError as e:
    973     # Catch JSON-related errors and raise as requests.JSONDecodeError
    974     # This aliases json.JSONDecodeError and simplejson.JSONDecodeError
--> 975     raise RequestsJSONDecodeError(e.msg, e.doc, e.pos)

JSONDecodeError: Expecting value: line 1 column 1 (char 0)

Originally posted by @patudom in #287 (comment)

[Carifio24]

@patudom Looks like this was a server-side issue which should be fixed with cosmicds/cds-api#77. Let me know if this pops up again.