the main fab icon doesn't appear

[MostafaKhaled2017]

I have made a fab icon that contains two nested fab icons but I don't know why the main fab icon which should open the other 2 fab icons doesn't appear and only the 2 nested fab icons appears above each others .

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>`