code: public void addMessageResolver(final IMessageResolver messageResolver) {
          Validate.notNull(messageResolver, "Message Resolver cannot be null");
          checkNotInitialized();
          this.messageResolvers.add(messageResolver);
      }
docs: <p>
  Adds a message resolver to the set of message resolvers to be used
  by the template engine.
  </p>
  <p>
  This operation can only be executed before processing templates for the first
  time. Once a template is processed, the template engine is considered to be
  <i>initialized</i>, and from then on any attempt to change its configuration
  will result in an exception.
  </p>
  
  @param messageResolver the new message resolver to be added.