code: public MapReduceOptions<T> map(final String map) {
          Assert.parametersNotNull("map", map);
          Assert.parameterNotEmpty("map", map);
          this.map = map;
          return this;
      }
docs: Set the JavaScript function that associates or "maps" a value with a key and emits the key and value pair.
  
  @param map the JavaScript function
  @return this