Why can't Scala find org.apache.commons.lang package?

I want to use org.apache.commons.lang.NotImplementedException as it seems to be the only NotImplementedException implementation in Java/Scala domain. I can remember I used to use it with Scala 2.8.1 with no hacks. But now it says "object lang is not a member of package org.apache.commons". Where has org.apache.commons.lang gone?