docs: public void apply(IntIntVector other, LambdaBinOpInt lambda, boolean skipZeros) {
          if (other instanceof IntIntSortedVector) {
              applyToSorted((IntIntSortedVector)other, lambda, false);
          } else if (other instanceof IntIntHashVector) {
              other = new IntIntSortedVector((IntIntHashVector) other);
              applyToSorted((IntIntSortedVector) other, lambda, false);
          } else if (other instanceof IntIntDenseVector) {
              other = new IntIntSortedVector((IntIntDenseVector) other);
              applyToSorted((IntIntSortedVector) other, lambda, false);
          } else {
              // TODO: we could just add a generic constructor. 
              throw new IllegalStateException("Unhandled vector type: " + other.getClass());
          }
      }