System.DmlException: Insert failed. First exception on row 0; first error: CANNOT_INSERT_UPDATE_ACTIVATE_ENTITY, APTS_OpportunityTrigger: execution of AfterInsert

caused by: System.DmlException: Update failed. First exception on row 0 with id 006S0000009qj2DIAQ; first error: CANNOT_INSERT_UPDATE_ACTIVATE_ENTITY, OpportunityAfterEventListener: execution of AfterUpdate

caused by: System.NullPointerException: Attempt to de-reference a null object

Trigger.OpportunityAfterEventListener: line 178, column 1: []

Class.OpportunityTriggerHelper.updatePriceBook: line 23, column 1
Class.OpportunityTriggerHandler.OnAfterInsert: line 7, column 1
Trigger.OpportunityTrigger: line 5, column 1: