Видео ютуба по тегу Type 'Null' Is Not A Subtype Of Type 'String' In My Flutter Cart Viewing Screen

What Causes the
What Causes the "type 'Null' is not a subtype of type 'String'" Error in Flutter TableCalendar?
Resolving the Null Type Subtype Error in Flutter's Cart Model
Resolving the Null Type Subtype Error in Flutter's Cart Model