Exception in thread Thread-2

I just ran into this issue/error: Exception in thread Thread-2 (background): Traceback (most recent call last): File "/usr/lib/python3.11/threading.py", line 1038, in _bootstrap_inner self.run() File "/usr/lib/python3.11/threading.py", line 975, in run self._target(*self._args, **self._kwargs) File "/home/nickp/enviroplusweb/enviroplusweb.py", line 469, in background update_readings() File "/home/nickp/enviroplusweb/enviroplusweb.py", line 356, in update_readings lcd_draw_readings() File "/home/nickp/enviroplusweb/enviroplusweb.py", line 142, in lcd_draw_readings if data_value > last_value * tolerance: ~~~~~~~~~~~^~~~~~~~~~~ TypeError: unsupported operand type(s) for *: 'NoneType' and 'float'

The service seems to be working in that I'm getting readings, but the readings aren't being logged and I'm not seeing graphs, despite having in run for about 4 hours.