Lua Error MasterMerchant

[Crystallize]

Hello, I have a problem with Master Merchant. The Addon worked fine till yesterday. Now the Addon doesn't load anymore. Reinstallation and deleting the SavedVariables doesn't work.

I always get this Lua Error:

user:/AddOns/MasterMerchant/MasterMerchant.lua:2918: attempt to index a nil value
stack traceback:
user:/AddOns/MasterMerchant/MasterMerchant.lua:2918: in function 'MasterMerchant:InitPurchaseHistory'
user:/AddOns/MasterMerchant/MasterMerchant.lua:2511: in function 'MasterMerchant:Initialize'
user:/AddOns/MasterMerchant/MasterMerchant.lua:3111: in function 'OnAddOnLoaded'

Does anybody know help?