docs: protected static <A, B> int size(NumberArrayAdapter<?, A> adapter1, A data1, NumberArrayAdapter<?, B> adapter2, B data2) {
      final int len = adapter1.size(data1);
      if(len != adapter2.size(data2)) {
        throw new IllegalArgumentException("Array sizes do not match!");
      }
      if(len == 0) {
        throw new IllegalArgumentException("Empty array!");
      }
      return len;
    }