code: public void update(T newValue, String configurationSourceName) throws IOException {
  		final String newValueAsString = valueConverter.toString(newValue);
  		configuration.save(key, newValueAsString, configurationSourceName);
  	}
docs: Updates the existing value with a new one
  
  @param newValue                the new value
  @param configurationSourceName the name of the configuration source that the value should be saved to
  @throws IOException                   if there was an error saving the key to the source
  @throws IllegalArgumentException      if there was a error processing the configuration key or value or the
  configurationSourceName did not match any of the available configuration
  sources
  @throws UnsupportedOperationException if saving values is not possible with this configuration source