Builders without a source annotation are applied to the analysed AST. It is very likely that these builders access the index and/or the task engine and it is a common mistake to forget setting these up before accessing them. This should be done automatically, before a builder strategy is called.

Submitted by Guido Wachsmuth on 2 April 2014 at 14:44

I will fix this as part of my refactoring at Oracle. Spoofax needs to be in charge of creating, loading and saving the index and task engine, not Stratego code in the project.