I am working in Trailhead on the "Learn CRM Essentials > Leads & Opportunities > Creating a Sales Process and Using Opportunities" module. I try to create the opportunity in the challenge and I get this error:
Apex script unhandled trigger exception by user/organization: 005360000024JQO/00D36000001DoTh
ClosedOpportunityTrigger: execution of AfterInsert
caused by: System.NullPointerException: Attempt to de-reference a null object
Trigger.ClosedOpportunityTrigger: line 9, column 1

What am I doing wrong? How do I fix this? Help.

I am working in Trailhead on the "Learn CRM Essentials > Leads & Opportunities > Creating a Sales Process and Using Opportunities" module. I try to create the opportunity in the challenge and I get this error:
Apex script unhandled trigger exception by user/organization: 005360000024JQO/00D36000001DoTh
ClosedOpportunityTrigger: execution of AfterInsert
caused by: System.NullPointerException: Attempt to de-reference a null object
Trigger.ClosedOpportunityTrigger: line 9, column 1

What am I doing wrong? How do I fix this? Help.