@Override public Item item(final QueryContext qc, final InputInfo ii) throws QueryException { final QNm name = toQNm(exprs[0], qc, sc, false); final long arity = toLong(exprs[1], qc); if (arity < 0 || arity > Integer.MAX_VALUE) throw FUNCUNKNOWN_X.get(ii, name); try { final Expr lit = Functions.getLiteral(name, (int) arity, qc, sc, ii); return lit == null ? null : lit.item(qc, ii); } catch (final QueryException e) { // function not found (in most cases: XPST0017) return null; } }