Graphql tool mergeSchemas throwing error if It gets more than 1 schema

I am trying to use graphql tool to perform schema stitching. However, if I pass more than one schema, it throws 2 error.

sometimes it throws

 Object.keys(source).forEach(key => {
                                        ^
RangeError: Maximum call stack size exceeded

Or

\'use strict';
^

RangeError: Maximum call stack size exceeded

My schema setup is pretty simple. I only have 2 schema Country and City. Those also have UUID, JSON scalar types.

import {
  makeExecutableSchema,
  mergeSchemas,
} from 'graphql-tools'
import GraphQLUUID from 'graphql-type-uuid'
import GraphQLJSON from 'graphql-type-json'

const countrySchema = makeExecutableSchema({
  typeDefs:`
    scalar UUID
    type Country {
      id: UUID!
      name: String
    }
    type Query {
      country: Country
    }
  `,
  resolvers: {
    UUID: GraphQLUUID,
  }
})


const citySchema = makeExecutableSchema({
  typeDefs:`
    scalar UUID
    scalar JSON
    type City {
      id: UUID!
      name: String
      coordinates: JSON
    }
    type Query {
      city: City
    }
  `,
  resolvers: {
    UUID: GraphQLUUID,
    JSON: GraphQLJSON,
  }
})


const resolvers = {
  Query: {
    country: () => ({ id: '2ij29fij390f3j', name: 'Toronto'}),
    city: () => ({id: '2ij29fij390f3j11', name: 'Toronto', coordinates: "[]"})
  }
}

export const schema = mergeSchemas({
  schemas: [ countrySchema, citySchema],
  resolvers: resolvers

});

Funny thing is that If I pass either countrySchema or citySchema to schemas array. It works. but both of them throws error I mentioned above.

Please share your thoughs.

This appears to be a regression introduced by version 6.0.0 of graphql-tools. Bump your version down to 5.0.0 by running npm install graphql-tools@5.0.0. If an issue hasn't been opened already, you can open one on Github for this bug.