value property Null safety

1. wings_data_model
2. wings_data_model
3. StreamUpdate<T>
4. value property

StreamUpdate class

1. Constructors
2. StreamUpdate
3. Properties
4. hashCode
5. props
6. runtimeType
7. stringify
8. value
9. Methods
10. noSuchMethod
11. toString
12. Operators
13. operator ==