private void checkFactoryNotNull(Object factory) {
   Preconditions.checkNotNull(factory, "factory cannot be null");
 }
  public void map(ChildAttributeResolver resolver, String attribute) {
    Preconditions.checkNotBlank(attribute, "Attribute cannot be empty");
    Preconditions.checkNotNull(resolver, "Resolver cannot be null");

    childAttributeResolvers.put(attribute, resolver);
  }
 private void checkViewAttributeClassNotNull(Class<?> viewAttributeClass) {
   Preconditions.checkNotNull(viewAttributeClass, "viewAttributeClass cannot be null");
 }