Ribbon 'guides' is None after session restore

[loic@…]

The following bug report has been submitted:
Platform:        Windows-10-10.0.18362
ChimeraX Version: 0.91 (2019-12-03)
Description
cartoon style modeHelix wrap command make all the atoms represented in cartoon disapear.

Log:
UCSF ChimeraX version: 0.91 (2019-12-03)  
© 2016-2019 Regents of the University of California. All rights reserved.  
How to cite UCSF ChimeraX  

> open "C:/Users/Loic/Desktop/Grimes_Lab/Manuscripts/ANP32 paper/Figure
> 2/Fig2d.cxs"

opened ChimeraX session  

> cartoon style modeHelix wrap

Traceback (most recent call last):  
File "C:\Program Files\ChimeraX_2\bin\lib\site-
packages\chimerax\core\triggerset.py", line 130, in invoke  
return self._func(self._name, data)  
File "C:\Program Files\ChimeraX_2\bin\lib\site-
packages\chimerax\atomic\structure.py", line 2661, in
_update_graphics_if_needed  
s[i]._update_graphics_if_needed()  
File "C:\Program Files\ChimeraX_2\bin\lib\site-
packages\chimerax\atomic\structure.py", line 304, in
_update_graphics_if_needed  
self._create_ribbon_graphics()  
File "C:\Program Files\ChimeraX_2\bin\lib\site-
packages\chimerax\atomic\structure.py", line 755, in _create_ribbon_graphics  
helix_ranges, sheet_ranges)  
File "C:\Program Files\ChimeraX_2\bin\lib\site-
packages\chimerax\atomic\structure.py", line 1073, in _smooth_ribbon  
ribbon_adjusts, start, end, p)  
File "C:\Program Files\ChimeraX_2\bin\lib\site-
packages\chimerax\atomic\structure.py", line 1411, in _wrap_helix  
guides[start:end] = coords[start:end] + directions  
TypeError: 'NoneType' object does not support item assignment  
  
Error processing trigger "graphics update":  
TypeError: 'NoneType' object does not support item assignment  
  
File "C:\Program Files\ChimeraX_2\bin\lib\site-
packages\chimerax\atomic\structure.py", line 1411, in _wrap_helix  
guides[start:end] = coords[start:end] + directions  
  
See log for complete Python traceback.  
  

> show atoms

> select #1

66274 atoms, 66935 bonds, 16 pseudobonds, 3 models selected  

> show sel atoms




OpenGL version: 3.3.0 NVIDIA 436.30
OpenGL renderer: GeForce 940MX/PCIe/SSE2
OpenGL vendor: NVIDIA Corporation

[pett]

Reported by Loic Carrique

[Elaine Meng]

could not reproduce with tube-helix session

(1) saved in 0.91, restored in 0.91
(2) saved in 1.2 daily build, restored in 1.2 daily build

[Elaine Meng]

it might be from an older session file, but I couldn't reproduce with session saved in 0.91