code: public MapUpdate update(String key, MapUpdate builder)
      {
          BinaryValue k = BinaryValue.create(key);
          updates.add(new MapOp.MapUpdate(new MapOp.MapField(MapOp.FieldType.MAP, k), builder.getOp()));
          return this;
      }
docs: Update the map in Riak by adding/updating the map mapped to the provided key.
  <p>
  If there is no map referenced by the key, it is created
  <p>
  
  @param key the key the map is mapped to.
  @param builder the update to apply to the map the key is mapped to. If none exists it is created.
  @return a reference to this object.