KeyError from plot_calendar

[fonnesbeck]

My data borks the plotting function.

In [2]: plot_calendar(zip_path='/home/fonnesbeck/export_27070161.zip', year=2018)       
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---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<ipython-input-2-1c69642af8dd> in <module>
----> 1 plot_calendar(zip_path='/home/fonnesbeck/export_27070161.zip', year=2018)

~/anaconda3/envs/dev/lib/python3.6/site-packages/strava_calendar/strava_calendar.py in plot_calendar(zip_path, year, plot_size, n_cols, month_gap, col_gap, sport, label)
     57         sport,
     58         datetime.datetime(year, 1, 1),
---> 59         datetime.datetime(year + 1, 1, 1),
     60     )
     61 

~/anaconda3/envs/dev/lib/python3.6/site-packages/strava_calendar/data.py in get_data(zip_path, sport, start_date, end_date)
    109         data = {"activities": []}
    110         for strava_file in filter_files(zip_path, filters):
--> 111             data["activities"].append(strava_file.to_json())
    112         with open(filename, "w") as buff:
    113             json.dump(data, buff)

~/anaconda3/envs/dev/lib/python3.6/site-packages/strava_calendar/data.py in to_json(self)
     49         return {
     50             "distance": self.session_data["total_distance"],
---> 51             "elapsed_time": self.session_data["total_timer_time"],
     52             "start_time": self.session_data["start_time"].isoformat(),
     53             "sport": self.session_data["sport"],

KeyError: 'total_timer_time'