GatewayState constructor Null safety

1. farmershands
2. gateway_state
3. GatewayState
4. GatewayState constructor

GatewayState class

1. Constructors
2. GatewayState
3. Properties
4. gateways
5. hashCode
6. hasListeners
7. runtimeType
8. Methods
9. addListener
10. dispose
11. fetchGateways
12. noSuchMethod
13. notifyListeners
14. removeListener
15. toString
16. Operators
17. operator ==