When importing a target group I'm getting this error. Any idea what's going on here?

error: anonymous.pp:31,22-32,14: cannot assign expression of type (null) to location of type   list(  { onDeregistration: output(string) | string, onUnhealthy: output(string) | string }
  | output({ onDeregistration: string, onUnhealthy: string }))
| output(list({ onDeregistration: string, onUnhealthy: string }))?: ;

Running command as

pulumi import aws:alb/targetGroup:TargetGroup <name> <arn>