the main fab icon doesn' appear

[MostafaKhaled2017]

I have made a main fsb icon that contains 2 nested fab icons that should be opened on press on the main fab icon but J found that the main fab icon doesn't appear and only the 2 nested fabs appear above each other.

this is my code :

<com.wangjie.rapidfloatingactionbutton.RapidFloatingActionLayout
    xmlns:rfal="http://schemas.android.com/apk/res-auto"
    android:id="@+id/multiple_actions"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintBottom_toTopOf="@id/navigation"
    rfab:rfab_drawable="@drawable/rfab__drawable_rfab_default"
    rfal:rfal_frame_color="#ffffff"
    rfal:rfal_frame_alpha="0.7">

    <com.wangjie.rapidfloatingactionbutton.RapidFloatingActionButton
        xmlns:rfab="http://schemas.android.com/apk/res-auto"
        android:id="@+id/fabChallenge"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        rfab:rfab_size="normal"
        rfab:rfab_drawable="@drawable/elect"
        rfab:rfab_color_normal="#37474f"
        rfab:rfab_color_pressed="#263238" />
    <com.wangjie.rapidfloatingactionbutton.RapidFloatingActionButton
        xmlns:rfab="http://schemas.android.com/apk/res-auto"
        android:id="@+id/fabAddPost"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        rfab:rfab_size="normal"
        rfab:rfab_drawable="@drawable/rfab__drawable_rfab_default"
        rfab:rfab_color_normal="#37474f"
        rfab:rfab_color_pressed="#263238"
        rfab:rfab_shadow_radius="7dp"
        rfab:rfab_shadow_color="#999999"
        /> 
</com.wangjie.rapidfloatingactionbutton.RapidFloatingActionLayout>