CUP-based parser classes are missing after switching git branch

[fnunnari]

After changing GIT branch, running VSM editor from the IntelliJ editor causes:
Caused by: java.lang.ClassNotFoundException: de.dfki.vsm.model.scenescript.CUP$ScriptParser$actions
and the window remains blank.
This happens only after trying to open a project (the main welcome screen shows correctly).

I guess this happens because after changing branch classes are normally deleted.
The classes for the CUP-based parser need to be re-generated from the grammar description, but this doesn't happen automatically.
When running, classes are there, but not for CUP stuff.

A workaround is to first run gradle clean, followed by gradle classes.