Right now the CurveTween constructor looks like this:

  /// Creates a curve tween.
  ///
  /// The [curve] argument must not be null.
  CurveTween({ @required this.curve })
    : assert(curve != null);

Usage currently looks like this:

CurveTween(curve: Curves.easeInOut);

There is a single required parameter, and I think it's quite certain that a CurveTween needs a Curve to function.

I propose to make it a regular parameter to make usage easier and a bit more fail-safe:

CurveTween(Curves.easeInOut);

If this is approved by the Flutter team, I will create a PR.