Filter end actions for null, and allow Runnables from Java

     * animation is explicitly canceled, use [addEndListener]. End listeners have an allEnded param,

     * which indicates that all relevant animations have ended.

     */

    fun withEndActions(vararg endActions: EndAction): PhysicsAnimator<T> {

        this.endActions.addAll(endActions)

    fun withEndActions(vararg endActions: EndAction?): PhysicsAnimator<T> {

        this.endActions.addAll(endActions.filterNotNull())

        return this

    }

    /**

     * Helper overload so that callers from Java can use Runnables or method references as end

     * actions without having to explicitly return Unit.

     */

    fun withEndActions(vararg endActions: Runnable?): PhysicsAnimator<T> {

        this.endActions.addAll(endActions.filterNotNull().map { it::run })

        return this

    }