default R hasSize(int size) {
    UnaryOperator<Expression> expr = e -> Expressions.binaryCall(IterableOperators.HAS_SIZE, e, Expressions.constant(size));
    return Matchers.extract(this).applyAndCreateRoot(expr);
  }
Match iterable attribute to be NOT empty (equivalent to {@code iterable.size() > 0})
criteria/common/src/org/immutables/criteria/matcher/IterableMatcher.java