Dropdown Menu based on List, A non-null String must be provided to a Text widget - flutter

Question

I am trying to generate a list of dropdown options for my user. I have created a custom model to use and here it is:
class UserFontModel {
String fontFamily;
FontWeight fontWeight;
UserFontModel({this.fontFamily, this.fontWeight});
}
I then create an instance here:
List<UserFontModel> _fonts = [
UserFontModel(fontFamily: 'Bold', fontWeight: FontWeight.w700),
UserFontModel(fontFamily: 'Medium', fontWeight: FontWeight.w500),
UserFontModel(fontFamily: 'Regular', fontWeight: FontWeight.w400),
UserFontModel(fontFamily: 'Light', fontWeight: FontWeight.w300),
UserFontModel(fontFamily: 'Thin', fontWeight: FontWeight.w100),
];
I then create a dropdown menu with the items based on the above list:
new DropdownButton<String>(
hint: Text('Style'),
items: _fonts.map((fonts) => DropdownMenuItem<String> (
child: Container(
width: MediaQuery.of(context).size.width * 0.2,
child: Text(fonts.fontFamily, style: TextStyle(fontWeight: fonts.fontWeight),),
),
)).toList(),
onChanged: (String _) {
setState(() {
print(_);
});
},
),
But for some reason (probably a simple one that i'm missing), I can't work out why i'm getting the error:
A non-null String must be provided to a Text widget.
Any thoughts?

Answer 1

Well, my obvious thought is: post a minimal compilable example, with the full error message.
But another thought that might actually help you to find the mistake yourself is: don't make programming hard on yourself. You are human. Let the machine do the hard work, that is the way we should do this. You want to make sure you never accidentally have a null value in your models? Then write the model so a null value is not possible without your compiler telling you exactly where you failed at compile time:
class UserFontModel {
final String fontFamily;
final FontWeight fontWeight;
const UserFontModel({#required this.fontFamily, #required this.fontWeight})
: assert(fontFamily != null),
assert(fontWeight != null);
}
This class is not instatiable without both fontFamily and fontWeight given, it will warn you at runtime, if you gave one and it was null and it makes sure you cannot accidentally change the fields after they have been checked to be correct. The point here is: this is your compiler. the machine does the work for you. As it should be.
This will not fix your actual problem, but it should fix your problem of not finding your actual problem.