**How to reproduce:**
1. Add Cryptomatte Node
2. Enable 'Object' render passes
3. Connect Cryptomatte to output (composite or viewer node)
4. Optional: set matte ID
5. (Do not connect input image)
6. Render
7. Observe invalid output image (or assert in debug build)
(see also PR for an example blend file)
Only CPU is affected. The solution follows the behavior of the GPU backend, where the input color of the single value input image is multiplied with the matte result to produce a non constant output.
Pull Request: https://projects.blender.org/blender/blender/pulls/135786
9fd67803dc