Answer
Check your customization's enumeration model files for a mismatched/incorrect Component assignment — in a confirmed case, an enumeration model file had its Component set incorrectly, and correcting it to the actual owning component (matching the rest of the customization) resolved the NullPointerException and let Clean and Build complete successfully. A build failure like this that follows a clean code-generation step is worth checking against your enumeration (and other) model files' Component settings before assuming a deeper environment or tooling problem.