ArmorStands unable to be summoned
Now with the new release of minecraft 1.11 coming up I decided to make an llama wearing a hat (this sounds really weird).
so I did /summon ArmorStand {}

but... it just said "Unable to summon object"
I also tried targeting an armorstand with /entitydata /execute /testfor and more but it said "Entity type 'minecraft:armorstand' is invalid". and I checked twice if I've done something wrong.

Steps to Reproduce:
1. just simply do /summon Armorstand in the 16w39snapshot note:I don't really know if this is a bug but I wan't it fixed in the final release...
2. ...
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