code: private void setInternal(String key, String value) {
  		Preconditions.checkArgument(value != null && !value.isEmpty(),
  			"The configuration value must not be empty.");
  
  		configuredOptions.put(key, value);
  	}
docs: Sets the configuration with (key, value) if the key is predefined, otherwise throws IllegalArgumentException.
  
  @param key The configuration key, if key is not predefined, throws IllegalArgumentException out.
  @param value The configuration value.