menu.findItem returns null

finally i found the problem:

I changed the last line in my /res/menu/sales.xml from:

<menu xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto" >
<!-- Search Widget -->
<item android:id="@+id/search_view_productos"
    android:title="@string/action_search"
    android:icon="@drawable/ic_action_search"
    app:showAsAction="always|collapseActionView"
    android:actionViewClass="android.widget.SearchView" />
</menu>

to this:

<menu xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto" >
<!-- Search Widget -->
<item android:id="@+id/search_view_productos"
    android:title="@string/action_search"
    android:icon="@drawable/ic_action_search"
    app:showAsAction="always|collapseActionView"
    app:actionViewClass="android.widget.SearchView" />
</menu>

Problem was the xml namespace on actionViewClass