Error:(10, 17) Resource id cannot be an empty string (at 'id' with value '@+id/').

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_fun_fact);
}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.fun_fact, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".FunFactsActivity"
    android:background="#ff51b46d"
    android:id="@+id/relativeLayout">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Did you know?"
        android:textSize="24sp"
        android:textColor="#80ffffff" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:text="Ants stretch when they wake up in the morning"
        android:id="@+id/factTextView"
        android:layout_centerVertical="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:textSize="24sp"
        android:textColor="@android:color/white" />

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Show Another Fun Fact"
        android:id="@+id/showFactButton"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"
        android:background="@android:color/white"
        android:textColor="#ff51b46d" />

</RelativeLayout>