public static function validate(Entity $entity)
 {
     $tag = "EntityValidator::validate()";
     Log::notice("{$tag}");
     $blueprint = $entity->blueprint();
     $errs = array();
     foreach ($blueprint->fields() as $field) {
         $key = $field->getKey();
         if ($err = EntityValidator::validateField($entity, $key)) {
             $errs["{$key}"] = $err;
         }
     }
     // log errors
     foreach ($errs as $key => $err) {
         Log::warning("{$tag}: [{$key}] {$err}");
     }
     return $errs;
 }