Adding a new Glyph to one of the sources causes issues

[colinmford]

Traceback (most recent call last):
  File "lib/eventTools/eventManager.pyc", line 165, in callObserver_withMethod_forEvent_withInfo_
  File "/Applications/RoboFont 2.app/Contents/Resources/lib/python3.9/mojo/subscriber.py", line 1666, in _roboFontCallback
  File "/Applications/RoboFont 2.app/Contents/Resources/lib/python3.9/mojo/subscriber.py", line 3343, in start
  File "/Applications/RoboFont 2.app/Contents/Resources/lib/python3.9/mojo/subscriber.py", line 3360, in fire
  File "/Applications/RoboFont 2.app/Contents/Resources/lib/python3.9/mojo/subscriber.py", line 1684, in _roboFontCoalescerCallback
  File "main.py", line 752, in roboFontDidSwitchCurrentGlyph
  File "main.py", line 423, in reset
  File "main.py", line 462, in redrawView
  File "main.py", line 198, in getScaledGlyph
  File "/Users/jamieotelsberg/Library/Application Support/RoboFont/plugins/Transmutor.roboFontExt/submodules/MutatorScale/lib/mutatorScale/objects/scaler.py", line 262, in getScaledGlyph
  File "/Users/jamieotelsberg/Library/Application Support/RoboFont/plugins/Transmutor.roboFontExt/submodules/MutatorScale/lib/mutatorScale/objects/scaler.py", line 286, in _getInstanceGlyph
  File "/Users/jamieotelsberg/Library/Application Support/RoboFont/plugins/Transmutor.roboFontExt/submodules/MutatorScale/lib/mutatorScale/objects/scaler.py", line 300, in _getInstance
AttributeError: 'IndexError' object has no attribute 'message'