Header of NavigationView not showing unless there is margin to top

I am creating an Android app which got a navigation drawer in a layout:

<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.DrawerLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <include
        layout="@layout/navigation_select_layout"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

    <android.support.design.widget.NavigationView
        android:id="@+id/nav_view"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        android:fitsSystemWindows="true"
        app:headerLayout="@layout/navigation_drawer_header_layout"
        app:menu="@menu/main_drawer_options" />
</android.support.v4.widget.DrawerLayout>

the navigation_drawer_header_layout:

<?xml version="1.0" encoding="utf-8"?>

<RelativeLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical">

    <TextView
        android:id="@+id/textViewButtonCloseDrawer"
        android:layout_width="30dp"
        android:layout_height="30dp"
        android:layout_alignParentRight="true"
        android:gravity="center"
        android:text="X"/>
</RelativeLayout>

The header layout is added but not showing unless I add either a top margin for the TextView or some padding to the RelativeLayout which pushes the TextView down.

Why won't it show as defined in the header layout? Why is the need to push the layout in order for it to be shown?