Iron Gollem NO damage

I was testing out a villager farm (were you place a lot of doors) in my creative test world. Naturally iron gollems would spawn, and mine did as well. Tho when i went in survival and he tried to hit me (because i killed one of his villagers) he couldn't damage me. he just moved his arms very fast.
I also didn't get any knock back.

I forgot to type F3+C (sorry for that)