Android : Line shape doesn't appear in Android API 21

I'm trying to make a line shape in android .. it works fine in all android versions except API 21

please help

<shape xmlns:android="http://schemas.android.com/apk/res/android" android:shape="line">

<size
    android:height="3px"
    android:width="10px" />
<stroke android:color="@color/brightPurple" />