code: public final BuilderType addDialogValidator(@NonNull final DialogValidator validator) {
          Condition.INSTANCE.ensureNotNull(validator, "The validator may not be null");
          getProduct().addDialogValidator(validator);
          return self();
      }
docs: Adds a new validator, which should be executed when the positive button of the dialog, which
  is created by the builder, is clicked.
  
  @param validator
  The validator, which should be added, as an instance of the type {@link
  DialogValidator}. The validator may not be null
  @return The builder, the method has been called upon, as an instance of the generic type
  BuilderType