3D Labels breaking session restore

[Elaine Meng]

open 1gcn
use right mouse mode to add a residue label
save session
(close models)
restore that session:

Unable to restore session, resetting.

Traceback (most recent call last):
File "/Users/pett/src/chimerax/ChimeraX.app/Contents/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/chimerax/core/session.py", line 579, in restore
obj = sm.restore_snapshot(self, data)
File "/Users/pett/src/chimerax/ChimeraX.app/Contents/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/chimerax/label/label3d.py", line 380, in restore_snapshot
s.set_state_from_snapshot(session, data)
File "/Users/pett/src/chimerax/ChimeraX.app/Contents/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/chimerax/label/label3d.py", line 392, in set_state_from_snapshot
ld[o] = ol = cls(o, v, kw)
TypeError: 'NoneType' object is not callable

[Tom Goddard]

Works with my current developer build. Appears to be fixed.

Get this error in April 23 build. Builds have been broken for a week due to code signing problem.

I notice that if I quit ChimeraX and restore the session with 3D label with the April 23 build then it works. So somehow the old closed models cause the new session restore to fail.

[Eric Pettersen]

This is somehow related to the import hook producing multiple instances of the Residue class! (maybe!)

[Eric Pettersen]

Fixed, for now.