code: public void addMeasure(Key key, int value) {
  
          if (key != null) {
              measures.put(key, value);
          } else {
              // TODO for now, we just ignore the value
          }
      }
docs: Adds a measure. If the key is <code>null</code>, the measure is simply
  ignored without any warning.
  
  @param key the key of the measure to be added to hash map
  @param value the value of the measure to be added to hash map