We must use a custom fucntion in the deltaQuery, but the passed in Context is always null, preventing any variable resolution.
In full-import mode behavior is correct.
Looking into the sources showed that the Conext is used from a thread-local Context.CURRENT_CONTEXT.get(),
wich is never set by (Context.CURRENT_CONTEXT.set()) for the Context created in DocBuilder.java:871
SOLR-2463 Using an evaluator outside the scope of an entity results in a null context
- is superceded by
SOLR-14783 Remove DIH from 9.0