Constraint Layout 2.0 alpha1 CustomAttribute has an error with attributeName="Alpha" about views-widgets-samples HOT 2 OPEN

<Transition
    motion:constraintSetEnd="@id/start"
    motion:constraintSetStart="@id/end"
    motion:duration="1000">
    <OnSwipe
        motion:dragDirection="dragDown"
        motion:touchAnchorId="@+id/view"
        motion:touchAnchorSide="bottom" />
</Transition>


<ConstraintSet android:id="@+id/start">
    <Constraint
        android:id="@+id/view"
        android:layout_width="100dp"
        android:layout_height="100dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="16dp"
        android:layout_marginEnd="8dp"
        motion:layout_constraintEnd_toEndOf="parent"
        motion:layout_constraintStart_toStartOf="parent"
        motion:layout_constraintTop_toBottomOf="@+id/toolbar">

        <CustomAttribute
            motion:attributeName="alpha"
            motion:customFloatValue="1.0" />
    </Constraint>
</ConstraintSet>

<ConstraintSet android:id="@+id/end">
    <Constraint
        android:id="@+id/view"
        android:layout_width="100dp"
        android:layout_height="100dp"
        android:layout_marginStart="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginBottom="16dp"
        motion:layout_constraintBottom_toBottomOf="parent"
        motion:layout_constraintEnd_toEndOf="parent"
        motion:layout_constraintStart_toStartOf="parent">

        <CustomAttribute
            motion:attributeName="alpha"
            motion:customFloatValue="0.0" />
    </Constraint>
</ConstraintSet>