suspendedProgram property Null safety

1. jrpn
2. model
3. ProgramMemory<OT extends ProgramOperation>
4. suspendedProgram property

ProgramMemory class

1. Constructors
2. ProgramMemory
3. Properties
4. bytesToNextAllocation
5. currentLine
6. hasExtended
7. hashCode
8. isRunning
9. lines
10. listing
11. memory
12. programBytes
13. programListener
14. returnStackPos
15. returnStackUnderflow
16. runner
17. runtimeType
18. suspendedProgram
19. Methods
20. adjustStackForRunStopStarting
21. debugReturnStack
22. decodeJson
23. deleteCurrent
24. displayCurrent
25. doNextIf
26. getAllInstructions
27. getCurrent
28. gosub
29. goto
30. gotoOpCode
31. importProgram
32. importProgramFromFile
33. incrementCurrentLine
34. insert
35. noSuchMethod
36. opcodeAt
37. popReturnStack
38. reset
39. resetReturnStack
40. skipIfRunning
41. stepCurrentLine
42. toJson
43. toString
44. Operators
45. operator ==
46. operator []