Image Writer fails on Images with lower case dimension labels

[Treiblesschorle]

The Image Writer node throws Exceptions (depending on the write format, I tested png, tif, jpeg) if the image to write has lower case dimension labels.

Steps to reproduce:

1. Create three equal size two dim images using the Image Generator
2. Merge and enter "x,y,Channel" into the Result Dimension Names of the Merger config
3. Try to write using the Image Writer in png or tif or jpeg