Fix/tidy signin success line - #5

The run was canceled by @gismofx.

The run was canceled by @gismofx.

The operation was canceled.

Possible null reference argument for parameter 'value' in 'Claim.Claim(string type, string value)'.

Dereference of a possibly null reference.

Possible null reference argument for parameter 'email' in 'Task<CustomIdentityUser?> UserManager<CustomIdentityUser>.FindByEmailAsync(string email)'.

Cannot convert null literal to non-nullable reference type.

Dereference of a possibly null reference.

Possible null reference argument for parameter 'key' in 'bool Dictionary<string, CustomIdentityUser>.TryGetValue(string key, out CustomIdentityUser value)'.

Dereference of a possibly null reference.

Possible null reference argument for parameter 'key' in 'bool Dictionary<string, CustomIdentityUser>.TryGetValue(string key, out CustomIdentityUser value)'.

Dereference of a possibly null reference.

Dereference of a possibly null reference.