fix: description not null

app/Http/Controllers/BreathingExerciseController.php

@@ -92,6 +92,8 @@ public function getTemplates()
             } else {
                 $template->image_url = null;
             }
+            // Old app expects a non-null description string.
+            $template->description = $template->description ?? '';
             return $template;
         });
 
@@ -109,6 +111,8 @@ public function getUserTemplates()
             } else {
                 $template->image_url = null;
             }
+            // Old app expects a non-null description string.
+            $template->description = $template->description ?? '';
             return $template;
         });