I'm trying to expose a service with Google Container Engine using the following command:

kubectl expose rc image-server --create-external-load-balancer=true

This fails to create the load balancer with the following output from 'kubectl describe services':

"Error creating load balancer (will retry): Failed to create load balancer for service default/image-server: failed to create target pool a06ecdc229dce11e5a90f42010af0004: googleapi: Error 400: Invalid value for: None is not a valid value, invalid"

Does anyone know why it's failing to create the target pool and/or what the "Invalid value for: None is not a valid value, invalid" error message might be referring to?