(: 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('')]