I am Getting the  below error while performing challenge on trailhead and the refrence error id is : YGLVGUOF
Please help me in this.

Hi there, I 'm trying to complete the "Automating Processes with the Lightning Process Builder" challenge in TrailHead but I get the following error :
Encountered unhandled fault when running process Update_contact_adress/
301240000004FXO exception by user/organization: 00D24000000JsNt/{4}

The flow failed to access the value for myVariable_current.Account.ShippingCountry because it hasn't been set or assigned.
caused by element : FlowRecordUpdate.myRule_1_A1
caused by: The flow failed to access the value for myVariable_current.Account.ShippingCountry because it hasn't been set or assigned.
Salesforce Error ID: 490660201-42718 (736882147)

Any idea what could be could wrong ?