Sybren A. Stüvel
4d0643a185
The issue is that `something.path_resolve('"custom_property"')` raises a
`ValueError` when the custom property is set to `None`. Since `None`
cannot be stored in a keyframe anyway, the property is now silently
skipped. Not having an explicit value is the closest we can get to
`None`. This of course breaks when the value should be `None` in between
not-`None` values, but I would consider that as a problem with the rig,
and not something Blender can fix.