Make cmpCustImage nullable in LoginResponseModel and stop requiring it in the constructor so missing images from the API are accepted. Handle potential nulls in OTPScreenController by coalescing to an empty string when assigning to UserProfileController.cmpCustImage. Update login screen logo asset path/size and remove the BoxFit, and simplify the sign-up first name hint/label from "User First Name" to "First Name". (pubspec.lock was also updated.)
