Neither the damage nor the post-explosion stun of Epoch Guardian's R pierce Spell Immunity despite being Pure damage and also Black Hole

[DeckardCainRPC]

STEPS TO REPRODUCE:

1. cast his R on something that doesn't have BKB
2. observe that they take damage from the spell, and also, they are frozen for a few seconds after the spell explodes at the end
3. now try it on something with BKB
4. they take no damage from the spell (despite being frozen in the black hole while it's being channeled)
5. also, when the spell explodes at the end, they are not frozen for a few seconds