This is a very generic error thrown when an application is trying to work with a reference that doesn't point to any object. There is no universal solution - you must find the cause in your particular case and fix it, e.g. adding code initializing the variable or running the code using the object only if it's actually set.
Hi, This error is too general and usually requires debugging to determine the specific cause. Have you customized your environment? You need to provide specific information so more people can help you troubleshoot. Best Regards, Hana