Add null safety (that shipped with the latest version of dart) and migrate to flutter V2

[nb9960]

[dev-raj-1729]

Hey I would like to work on this

[Vikhyath08]

Sure! All Yours. Make sure you read up well on Null Safety beforehand and perform extensive testing so as to not break any existing functionality. Also, Feel free to clarify any point which you feel is confusing, as this is a major issue.