Android: CardView foreground using databinding

I'm trying to fill my RecyclerView with CardViews, the CardViews use Android databinding to set Attributes like Texts in TextViews. On Items that aren't finished jet I want to add a greyish overlay. But unfortunately the foreground android:foreground="@{viewModel.getState != State.FINISHED? @color/gray_transparent54 : null}"> is not applied. On the other hand, if I force the foreground color android:foreground="@grey_transparent54">, it works it is.

<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools">
    <data class="ListItemBinder">
        <import type="myProject.State"/>
        <import type="android.view.View"/>
        <variable
            name="viewModel"
            type="myProject.ListItemViewModel"/>
    </data>

    <android.support.v7.widget.CardView
        xmlns:card_view="http://schemas.android.com/apk/res-auto"
        android:layout_width="match_parent"
        android:layout_height="80dp"
        card_view:cardCornerRadius="4dp"
        android:foreground="@{viewModel.getState != State.FINISHED? @color/gray_transparent54 : null}">
            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="@{viewModel.getName}"
                tools:text="Name"
                android:textColor="@color/color_text_primary"
                android:textSize="24sp"/>
    </android.support.v7.widget.CardView>
</layout>

Thanks in advance.