Panic in Publicize when using Hash(Integer, PayloadType)

[luna-duclos]

When using a Hash(Integer, PayloadType) goa generates a map[int]*PayloadType, which is correct.
However, in the Publicize function of the generated code in user_types.go, the following is generated:

	if ut.Triggers != nil {
		pub.Triggers = make(map[int]*GameengineAchievementTriggerPayload, len(ut.Triggers))
		for k2, v2 := range ut.Triggers {
			pubk2 := k2
			pubv2 := v2.Publicize()
			pub.Triggers[pubk2] = pubv2
		}
	}

This causes a panic if the client sends a null value for v2