Hi everyone, I found a bug and used AI to narrow it down to the smallest possible reproducer. I hope this helps. ### schnipp (: Reproducer for BaseX bug: NPE in Single.has() via Step.get() Affected versions: 12.2, 12.3, 12.4 Not affected: 12.0, 12.1 Required conditions (all three necessary): 1. .[] step — Path.get() converts Filter(ContextValue, preds) to Step.get(SELF, preds) 2. compound `and` predicate — creates an Arr containing the FuncRef 3. imported module function as an operand — unresolved at parse time -> FuncRef(expr=null) FuncRef extends Single but has no has() override -> Single.has() NPEs on null expr Fix: add has() override to FuncRef inner class in StaticFuncs.java (analogous to accept()): @Override public boolean has(final Flag... flags) { return expr != null && expr.has(flags); } :) import module namespace functx = "http://www.functx.com"; <a/>/.[true() and functx:all-whitespace('')] ### schnapp Best regards, Andreas