How to use BottomAppBar with BottomNavigationView inside in a Single Activity App Architecture?

Question

I want to add a FloatingActionButton in the middle of BottomAppBar with curve below. So i Added tried to design the MainActivity like below. I maintained Single Activity Architecture in this app. Now, I have faced two problems.

1. If I want to set Visibility:gone for bottomappbar & floatingActionButtonin any particular fragment than both are gone but created an empty view. Like the screen shot. How can I remove that empty view?
2. I want to make transparent the gap between FloatingActionButton & BottomAppBar. But failed to do that.

This is the code below of my MainActivity's XML.

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".ui.MainActivity">

    <com.google.android.material.appbar.AppBarLayout
        android:id="@+id/appbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:fitsSystemWindows="true">
        <androidx.appcompat.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:background="@color/colorPrimary"
            android:theme="@style/ThemeOverlay.MaterialComponents.Dark.ActionBar" />

    </com.google.android.material.appbar.AppBarLayout>

    <fragment
        android:id="@+id/my_nav_host_fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginBottom="?attr/actionBarSize"
        app:defaultNavHost="true"
        app:layout_behavior="com.google.android.material.appbar.AppBarLayout$ScrollingViewBehavior"
        app:navGraph="@navigation/navigation_graph" />

    <com.google.android.material.bottomappbar.BottomAppBar
        android:id="@+id/bottomAppBar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom"
        app:fabCradleMargin="10dp"
        app:elevation="0dp"
        app:fabCradleRoundedCornerRadius="10dp"
        app:fabCradleVerticalOffset="10dp">

        <com.google.android.material.bottomnavigation.BottomNavigationView
            android:id="@+id/bottom_nav_view"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_marginEnd="16dp"
            android:background="@android:color/transparent"
            app:menu="@menu/navigation_menu" />

    </com.google.android.material.bottomappbar.BottomAppBar>

    <com.google.android.material.floatingactionbutton.FloatingActionButton
        android:id="@+id/fab_add"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:contentDescription="@string/app_name"
        android:src="@drawable/ic_dashboard_add"
        app:backgroundTint="@color/colorDashboardFloatingButton"
        app:tint="@color/colorWhite"
        app:layout_anchor="@id/bottomAppBar" />

</androidx.coordinatorlayout.widget.CoordinatorLayout>

Here are the screenshots.