code: public void put(final String key, final String value) {
          if (value == null) {
              throw new IllegalArgumentException("No value provided for key " + key);
          }
          validate(key, value);
          data.putValue(key, value);
      }
docs: Adds an item to the data Map.
  @param key The name of the data item.
  @param value The value of the data item.