Merging GraphQL Resolvers for Apollo Server not working with Object.assign()

I am modularizing my schema for a GraphQL API and trying to merge the resolvers without using any 3rd party libraries.

Is there a simple way to do this without Lodash.merge() or equivalent?

The Apollo Documentation says to use a library such as Lodash to merge() modularized resolvers. (http://dev.apollodata.com/tools/graphql-tools/generate-schema.html#modularizing)

The problem seems to be that by their nature, the resolvers contain functions as properties, so they seem to be omitted when I access them via Object.assign() or even JSON.stringify().

If I console.log them, I see: {"Query":{},"Mutation":{}}

Here is what one of the resolvers looks like:

 const productResolvers = {
   Query: {
     myProducts: (root, { userId }, context) => {
       return [
         { id: 1, amount: 100, expiry: '12625383984343', created: '12625383984343' },
         { id: 2, amount: 200, expiry: '12561351347311', created: '12625383984343' },
         { id: 3, amount: 200, expiry: '11346347378333', created: '12625383984343' },
         { id: 4, amount: 350, expiry: '23456234523453', created: '12625383984343' },
       ];
     },
   },
   Mutation: {
     addProduct: (root, { userId }, context) => {
       return { id: 350, amount: 100, expiry: '12625383984343', created: '12625383984343' };
     },
   }
 };

Let's assume there is another one virtually identical called widgetResolvers.

Here is a fully functional block of code:

 export const schema = makeExecutableSchema({
   typeDefs: [queries, mutations, productSchema, widgetSchema],
   resolvers
 });

Here is what I'm trying to achieve:

 export const schema = makeExecutableSchema({
   typeDefs: [queries, mutations, productSchema, widgetSchema],
   resolvers: Object.assign({}, productResolvers, widgetResolvers)
 });

I haven't loaded in ability to use rest spread yet (https://babeljs.io/docs/plugins/transform-object-rest-spread/). I suspect it won't work for the same reason Object.assign() doesn't work.

Oh, and here is why I suspect this merge doesn't work: Why doesn't JSON.stringify display object properties that are functions?