Short description: 
Uploading a single-player world with datapack causes realms uploader to dysfunction.

Steps to reproduce:

• Step 1
  Create a brand new world through the singeplayer menu and load the world by joining it.
• Step 2
  Enter the *\AppData\Roaming\.minecraft\saves[worldname]\datapacks directory

• Step 3
  Unpack your datapack folder in my case this datapack.
• Step 4
  In the Realms menu click the wrench to configure realm.
• Step 5
  Select Reset realm, click on upload world select our newly created world [worldname] with the datapack unpacked.

Expected result:
Prepares your world for uploading and then procedures to upload it to the realms server.

Actual result:
Gets stuck on Preparing your world... animation and never gets further.