NullReferenceException with PopulateLoot

Code:

NullReferenceException: Object reference not set to an instance of an object
  at LootContainer.PopulateLoot () [0x00000] in <filename unknown>:0
  at LootContainer.SpawnLoot () [0x00000] in <filename unknown>:0
  at LootContainer.ServerInit () [0x00000] in <filename unknown>:0
  at HackableLockedCrate.ServerInit () [0x00000] in <filename unknown>:0
  at BaseNetworkable.Spawn () [0x00000] in <filename unknown>:0
  at CH47HelicopterAIController.DropCrate () [0x00000] in <filename unknown>:0
  at CH47AIBrain+DropCrate.StateThink (Single delta) [0x00000] in <filename unknown>:0
  at BaseAIBrain`1[T].AIThink (Single delta) [0x00000] in <filename unknown>:0
  at CH47AIBrain.AIThink (Single delta) [0x00000] in <filename unknown>:0
  at CH47AIBrain.FixedUpdate () [0x00000] in <filename unknown>:0
(Filename:  Line: -1)