Can Imposter Ditto copy typeless Pokemon?

Question

I was playing a normal double battle (not ranked or vgc) and my Arcanine used Burn Up and obtained Wonder Guard from Shedinja. The next turn the opponent sent in an Imposter Ditto which should have copied my Arcanine and become typeless, but seems like it stayed as Normal Type since I was able to hit super effectively with Close Combat. What's the reason behind that? Imposter can't copy typeless?

Answer 1

If the Pokémon with this Ability transforms into a Pokémon that has no type (i.e. it was a pure Fire type that used Burn Up), the transformed Pokémon will become Normal-type; if such a Pokémon has additionally been affected by Forest's Curse or Trick-or-Treat, the user will become Normal-type with an added Grass or Ghost type respectively.

Source
So no, Imposter won't copy a typeless Pokemon and the transformed Pokemon stays as a Normal-type.