code: @Nullable
      public Object onActionPressed() {
          View existingForm = getExistingForm();
          if (existingForm == null) {
              return null;
          }
  
          FormView form = (FormView) existingForm;
          Object ev = form.submitForm();
          if (ev == null || lockWidget.getConfiguration().getExtraSignUpFields().size() <= SignUpFormView.MAX_FEW_CUSTOM_FIELDS) {
              return ev;
          } else if (existingForm == signUpForm) {
              //User has configured some extra SignUp custom fields.
              DatabaseSignUpEvent event = (DatabaseSignUpEvent) ev;
              showCustomFieldsForm(event);
              return null;
          }
          return ev;
      }
docs: ActionButton has been clicked, and validation should be run on the current
  visible form. If this validation passes, an action event will be returned.
  
  @return the action event of the current visible form or null if validation failed