code: public BrowserConfigurationOptions set(String key, String value) {
      if (value != null) {
        options.put(key, value);
      }
      return this;
    }
docs: Sets the given key to the given value unless the value is null. In that case, no entry for the
  key is made.
  
  @param key the name of the key
  @param value the value for the key
  @return this / self