error : “”Object reference not set to an instance of an object” when open SSRS Report

try one or all of this solutions below :
1. Generate Incremental CIL
2. Compile on the customized report including report class (Contract, controller, DP). If you have modified TMP table , please do synchronize on that table.
3. Clean User Usage data on Tools-> Option -> Usages Data.
4. Restarting reporting services.
5. Refresh all cache on AOT, on AOT-> Tools -> Caches
5. Re-Deploy the SSRS report.
6. Restarting AOS. << sometimes it works like magic -_-“