code: public void union(final HLL other) {
          // TODO: verify HLLs are compatible
          final HLLType otherType = other.getType();
  
          if(type.equals(otherType)) {
              homogeneousUnion(other);
              return;
          } else {
              heterogenousUnion(other);
              return;
          }
      }
docs: Computes the union of HLLs and stores the result in this instance.
  
  @param other the other {@link HLL} instance to union into this one. This
  cannot be <code>null</code>.