Improved support for null safety

[mit-mit]

A common source of programming faults are programs that unintentionally try to use values that are null. This issue requests Dart support for differentiating between nullable and non-nullable data types, paired with static validation.

Given vast amount of code already exists, it additionally requests a mechanism by which Dart packages and apps can gradually migrate to to utilize this.

UPDATE: this is being worked on as part of #110

[yjbanov]

I would strongly recommend that we also add a requirement that null safety is designed with unboxing in mind. Even though by itself it does not result in unboxing, it is a necessary first step for any future language evolution towards higher performance.

[dainmiller]

Maybe for this we can look at Swift's extreme success with optional types?

[mit-mit]

Closing this request issue as this is being worked on and tracked as feature #110