@Override public Expr optimize(final QueryContext qc, final VarScope scp) throws QueryException { super.optimize(qc, scp); final ExprList el = new ExprList(exprs.length); for (final Expr ex : exprs) { if (ex.isEmpty()) { // remove empty operands (return empty sequence if first value is empty) if (el.isEmpty()) return optPre(qc); qc.compInfo(OPTREMOVE_X_X, this, ex); } else { el.add(ex); } } // ensure that results are always sorted if (el.size() == 1 && iterable) return el.get(0); // replace expressions with optimized list exprs = el.finish(); return this; }