IconHelper constructor Null safety

1. diginote
2. icon_helper
3. IconHelper
4. IconHelper constructor

IconHelper class

1. Constructors
2. IconHelper
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. noSuchMethod
8. toString
9. Operators
10. operator ==
11. Static properties
12. addIcon
13. boldIcon
14. centreAlignIcon
15. colourPickerIcon
16. deleteIcon
17. editIcon
18. italicIcon
19. justifyAlignIcon
20. leftAlignIcon
21. listIcon
22. numberedListIcon
23. previewIcon
24. rightAlignIcon
25. scheduleIcon
26. screensIcon
27. settingsIcon
28. strikethroughIcon
29. templatesIcon
30. underlineIcon
31. zoomIn
32. zoomOut