Why do I get a Null pointer exception when the PL/I Editor opens up?
It is possible that the 'File System Mapping' has changed (for **PLI use *.pl1 instead of *.pli for example) and also the 'File Associations' for PL/I programs (Go to Window>Preferences>General>Editors>File associations and set the PL/I Editor to *.pl1 files),
When a user uses File Associations it tells the editors that it can open a particular file mapping, however it does not tell the editor what kind of file it is or what type of content that file mapping might have.
When using Content Types you are telling the editors that each one of these file mapping are all part of a particular type of file which allows the tooling with those editors to be enabled. This falls in line with the way Eclipse uses File Associations and Content Types.
Instead of using File Associations, use Content Types. If you go to Window -> Preferences -> General -> Content Types. Expand the Text category and there will be a Category for PL/1 Source Files. Add the *.pl1 extension here.
Content Types are a super set over File Associations and this will provide more tooling than just adding the File Associations.
Using Content Types is the recommended way for allowing customers to add custom mapping within RDz.