HTTP exception not giving a Json Response in custom module file

Question

I am using the Drupal REST module. I have a custom module file I have created and it has a hook below

function magri_rest_user_presave($account) {


   if (isset($account->field_region->value)) {


        $taxonomy_query = \Drupal::entityQuery('taxonomy_term');
        $taxonomy_query ->condition('vid', "region")
            ->condition('name', $account->field_region->value);
        $tids = $taxonomy_query->execute();

        $tid = array_values($tids)[0];


        if($tid){
            //set taxonomy ref field on user entity
            $account->field_region_tax->target_id = $tid;

        }else{
            throw new NotFoundHttpException(t('Region not found!'));

        }
    }

The exception is thrown but it only gets printed in the logs:

Symfony\Component\HttpKernel\Exception\NotFoundHttpException: Region not found! in magri_rest_user_presave() (line 61 of /var/www/html/modules/custom/magri_rest/magri_rest.module).

Symfony\Component\HttpKernel\Exception\HttpException: Internal Server Error in Drupal\rest\Plugin\rest\resource\EntityResource->post() (line 198 of /var/www/html/core/modules/rest/src/Plugin/rest/resource/EntityResource.php).

I want something like below to be returned to the client:

{
    "error":"Region not found!", 
}