FieldResolverError with resolver for superclass or interface #497

Description

Consider the following dataclass hierarchy:

abstract class Base {
}

class Thing extends Base {
}

This is a custom resolver for the abstract class Base:

class BaseResolver implements GraphQLResolver<Base> {
    public boolean isActive(Base base) {
       return true;
   }
}

Root query resolver with datafetcher that returns our concrete class Thing:

class RootQueryResolver implements GraphQLQueryResolver {
    public Thing getThing() {
        return new Thing();
    }
}

Expected behavior

The following schema should work fine and return true for queries on the active field:

type Query {
    thing: Thing!
}

type Thing {
    active: Boolean!
}

Actual behavior

graphql.kickstart.tools.resolver.FieldResolverError: No method or field found as defined in schema [...]

Steps to reproduce the bug

1. Create a resolver for a supertype (class or interface) with any datafetcher
2. Have a query return a subclass of that type
3. Try building the schema