Eliminating nullOk Parameters

Summary

Context

Description of change

Migration guide

Timeline

References

Summary

This migration guide describes conversion of code that uses the nullOk
parameter on multiple of static accessors and related accessors to use
alternate APIs with nullable return values.

Context

Flutter has a common pattern of allowing lookup of some types of widgets
(InheritedWidgets) using static member functions that are typically called
of, and take a BuildContext.

Before non-nullability was the default, it was useful to have a toggle on these
APIs that swapped between throwing an exception if the widget was not present in
the widget tree and returning null if it was not found. It was useful, and
wasn’t confusing, since every variable was nullable.