Controller constructor Null safety

1. jrpn
2. controller
3. Controller
4. Controller constructor

Controller class

1. Constructors
2. Controller
3. Properties
4. argBase
5. gotoLineNumberKey
6. gsbOperation
7. gtoOperation
8. hashCode
9. keyboard
10. lastKey
11. minusOp
12. model
13. multOp
14. runtimeType
15. state
16. Methods
17. buttonDown
18. buttonUp
19. buttonWidgetDown
20. delayForShow
21. getArgsAndRun
22. getErrorNumber
23. handlePSE
24. newSelfTests
25. noSuchMethod
26. pasteToX
27. reset
28. resetAll
29. showCalculatorError
30. showMessage
31. singleStep
32. toString
33. Operators
34. operator ==