Exception when using with GraphiQL

[IdeaHunter]

An exception of type 'GraphQL.Parser.SourceException' occurred in GraphQL.Parser.dll but was not handled in user code
Additional information: subscriptionType'' is not a field of type __Schema''
The query that graphiql uses:

  query IntrospectionQuery {
    __schema {
      queryType { name }
      mutationType { name }
      subscriptionType { name }
   }
  }