switched error handling over to middleware instead

backend/utils/NotValidDataError.ts

@@ -1,12 +1,10 @@
 class NotValidDataError extends Error {
   code: number;
-  isCustomError: boolean;
 
   constructor(args: any) {
     super(args);
 
     this.code = 403;
-    this.isCustomError = true;
   }
 }