According to documentation for Apollo’s GraphQL-tools:

You don’t need to specify resolvers for every type in your schema. If you don’t specify a resolver, GraphQL.js falls back to a default one…

The documentation goes on to state that the default resolver will look for a property on the parent object with the field name that’s being resolved. If that property is not a function, the value of the property is returned. But if the property does contain a function, then the default resolver calls it, and “passes the query arguments into that function.”

It wasn’t clear to me exactly what this meant, so I did some experimenting. Read more on Understanding the Apollo Default Resolver…