This item may not have a label readable by screen readers.

Quando editei o XML do Layout, fica no Component Tree, ao lado do floatingActionButton uma exclamação vermelha com esta mensagem "This item may not have a label readable by screen readers"

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ListView
        android:id="@+id/activity_main_lista_de_alunos"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

    <com.google.android.material.floatingactionbutton.FloatingActionButton
        android:id="@+id/floatingActionButton5"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentEnd="true"
        android:layout_alignParentBottom="true"
        android:layout_marginEnd="25dp"
        android:layout_marginBottom="25dp"
        android:clickable="true"
        app:srcCompat="@android:drawable/ic_menu_add" />

</RelativeLayout>