private static void Foo( System.Object obj ) {
	if ( null == obj ) {
		throw new System.NullArgumentException( "obj" );
	}
	// do something with obj
}
private static void Bar( System.Object obj ) {
#if DEBUG
	if ( null == obj ) {
		throw new System.NullArgumentException( "obj" );
	}
#endif
	// do something with obj
}