Android RecyclerView there is empty gap at the above of the items

Question

According to the attached picture, I'm experiencing an empty space with exactly one page height at the above the recyclerview items.

Here is my recyclerview row layout:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical">

    <android.support.v7.widget.CardView
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

         <RelativeLayout
            android:layout_width="match_parent"
            android:layout_height="50dp"
            android:background="@color/white">

            ...

        </RelativeLayout>

    </android.support.v7.widget.CardView>

</LinearLayout>

And this is my activity layout:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
    android:orientation="vertical">


    <include
        android:id="@+id/list_toolbar"
        layout="@layout/toolbar_list"></include>

    <android.support.v7.widget.RecyclerView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:scrollbars="vertical" />

        ...

I also tried layout_height="match_parent" for the recyclerview but the only difference was the empty gap shown at the first without any scrolling.
Setting fixed height to the items also didn't change anything.

Answer 1

After updating the dependencies to recyclerview-v7:25.3.1, I forced to change all row_items's layout_height from match_parent to wrap_content.
In this case I forgot to change the layout_height of an item_row layout which was my header row of the recyclerview.

Here is my recyclerview header row that should have layout_height="wrap_content":

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