@Nullable
    @Override
    public Invokable invoke(Invokation invokation, Object... params) {
      String indentationToResore = invokation.consumer.indentation;
      // switch to the current indentation inside fragment
      invokation.consumer.indentation = invokation.consumer.getCurrentIndentation().toString();
      run(new Invokation(invokation.consumer, params));
      invokation.consumer.indentation = indentationToResore;
      return null;
    }
@param arity number of fragment parameters
generator/src/org/immutables/generator/Templates.java