MVC Related bug

Question

Hello everyone.! I hope you're good in this pandemic with your health. I am fresher..I have made a project which was sign-up form with user and admin form. I have made a project in mvc. When I was Run my code form is open easily and when I click submit bottun some time it was successfully submitted. and data is added in my database. BUT SOMETIME THERE WAS A ERROR WHICH WAS.. object reference not set to an instance of an object. Please help me..as soon as possible