This may also help some people.
In my case, it was because I had not defined a context in the menu.xml
Try this:
<menu xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
tools:context="com.example.android.ActionBarActivity">
Instead of this:
<menu xmlns:android="http://schemas.android.com/apk/res/android">