In C#, when you try to access something that’s null, you’ll get a NullReferenceException.

The description will say

Object reference not set to an instance of an object.

It means that you’re trying to use something that hasn’t been initialized.

There can be multiple fixes to it, but I’ll advise you to look deeper into the logic of your program to find out the root cause.

Just inserting the if (something != null) check might work, but it’s unlikely a great long term solution.