Unexpected schema definition on "undefined"

[sesteva]

Hi when running the doc on a modularized schema, Im getting Unexpected schema definition on "undefined".

graphdoc -s ./src/schema/index.js -o ./doc/schema

index.js is transpile using babel via rollup

import Post from './models/Post';
import User from './models/User';
import resolvers from './resolvers'

const RootQuery = `
  type RootQuery {
    posts: [Post]
    post (id: Int!): Post
    users: [User]
    user: User
  }
`;

const SchemaDefinition = `      
  schema {
    query: RootQuery
  }
`;

export default makeExecutableSchema({
  typeDefs: [
    SchemaDefinition, RootQuery, Post, User
  ],  
  resolvers
});

node v8.11.2
npm 6.4.1

Thanks!