ID 148201 - Flipbook Ignores custom LUTs from the Comp Viewer

Problem summary
When setting Custom Viewer Processes, they do not get added to the Flipbook dialog. 

If you select a Custom Viewer Process when starting the export process, you will get an "Output color space index(25) out of range." Error.

Customer reported version
nuke.11.2v3

Customer reported platform

Steps to reproduce

1) Copy the attached Gizmo into your ~/.nuke directory

2) Add this line in your ~/.nuke/init.py file and save it: 

nuke.ViewerProcess.register("myLUT", nuke.Node, ("myLUT", ""))

3) Open Nuke, create a ColorWheel node

4) Select the ColorWheel node and from the top toolbar, navigate to "Render -> Flipbook Selected".

5) Within the 'LUT' field, select 'myLUT':

 ​​

6) Render the Flipbook by pressing 'OK'.

Result: The render will complete and in the Flipbook error with "Output color space index(25) out of range."  and the LUT dropdown will not contain the custom LUT:

Workaround
Unknown.

Reproduced by support
This bug has been reproduced in:

Nuke 11.3v1 - Windows 10, CentOS 7.9, MacOS 10.13

This was previously tested by QA

Expected behaviour
For the custom viewer process to be available in the Flipbook

Actual behaviour
The Flipbook errored with "Output color space index(25) out of range."  and the LUT dropdown did not contain the custom LUT