configurationVisitor.handleMissingPath: could not plan a field Mutation.__typename on a path mutation.__typename

[cs-clarence]

Mutations with __typename fails. I am using cosmo router but I posted it here because it looks like the underlying error is in graphql-go-tools
It seems that cosmo router doesn't support this kind of mutation:

mutation M {  
  __typename # mutations with this causes the error
  CreateUser() {
    __typename
    # skip
  }
}

In playground:

__typename on root query node works fine:

[vikstrous2]

I ran into the same issue with

query Q {
  __typename
}