reverseCurve property Null safety
The curve to use in the reverse direction.
If the parent animation changes direction without first reaching the AnimationStatus.completed or AnimationStatus.dismissed status, the CurvedAnimation stays on the same curve (albeit in the opposite direction) to avoid visual discontinuities.
If you use a non-null reverseCurve, you might want to hold this object in a State object rather than recreating it each time your widget builds in order to take advantage of the state in this object that avoids visual discontinuities.
If this field is null, uses curve in both directions.