diff --git a/src/lessons/lessons.service.ts b/src/lessons/lessons.service.ts
index 1d2706d..36fb49d 100644
--- a/src/lessons/lessons.service.ts
+++ b/src/lessons/lessons.service.ts
@@ -85,7 +85,8 @@ export class LessonsService {
               endOutputType: 'utc',
             } as EventAttributes),
         )
-        .concat([this.createMaintenanceEvent()]),
+        .concat([this.createMaintenanceEvent()])
+        .filter((e) => e),
     );
 
     if (error) {