Asp.net core identity method FindByEmailAsync throws exception

Question

I'm using .net core 5 and identity core, my project was working fine until I start getting errors in FindByEmailAsync method

 identityUser = await userManager.FindByEmailAsync(userinfo.Email);

Exception: Data is Null. This method or property cannot be called on Null values.

and here is the stacktrace of Microsoft code:

   at Microsoft.Data.SqlClient.SqlBuffer.ThrowIfNull()
   at Microsoft.Data.SqlClient.SqlBuffer.get_String()
   at Microsoft.Data.SqlClient.SqlDataReader.GetString(Int32 i)
   at Microsoft.EntityFrameworkCore.Query.Internal.SingleQueryingEnumerable`1.AsyncEnumerator.<MoveNextAsync>d__14.MoveNext()
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.ConfiguredValueTaskAwaitable`1.ConfiguredValueTaskAwaiter.GetResult()
   at Microsoft.EntityFrameworkCore.Query.ShapedQueryCompilingExpressionVisitor.<SingleOrDefaultAsync>d__15`1.MoveNext()
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at Microsoft.EntityFrameworkCore.Query.ShapedQueryCompilingExpressionVisitor.<SingleOrDefaultAsync>d__15`1.MoveNext()
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at Microsoft.AspNetCore.Identity.UserManager`1.<FindByEmailAsync>d__116.MoveNext()
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()

note that userManger , userinfo and userinfo.Email are not null.

Answer 1

I found the problem. I had added the following properties to the IdentityUser user:

   public class AppIdentityUser : IdentityUser<int>
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
    }

and they had null values for the user I was selecting by email. And I changed them to nullable string and the problem was solved(after appltying migration).

        public string? FirstName { get; set; }
        public string? LastName { get; set; }