How to write resolver for union types?

[Jaay7]

Example that I tried to implement

demo.graphqls

type School {
  id: ID!
  name: String!
  description: [String]
  contactInfo: String!
  address: String!
  standard: [String]
  board: String!
}

type College {
  id: ID!
  name: String!
  description: [String]
  contactInfo: String!
  address: String!
  course: [String]
}

union SearchResults = School | College

type Query {
  searchResults(val: String): [SearchResults]
}

Since I'm using MongoDB

SchoolRepository.java

package com.example.demo.repository;

import com.example.demo.model.School;

import org.bson.types.ObjectId;
import org.springframework.data.mongodb.repository.Query;
import org.springframework.data.mongodb.repository.MongoRepository;

public interface SchoolRepository extends MongoRepository<School, String> {
  @Query("{ 'name': { $regex: ?0, $options: 'i' } }")
  Iterable<School> find(String val);
}

Similar to this I wrote College repository too.

Query.java

package com.example.demo.resolver;

import java.util.*;
import com.example.demo.model.School;
import com.example.demo.model.College;
import com.example.demo.repository.SchoolRepository;
import com.example.demo.repository.CollegeRepository;
import com.coxautodev.graphql.tools.GraphQLQueryResolver;
import org.bson.types.ObjectId;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

@Component
public class Query implements GraphQLQueryResolver {
  private SchoolRepository schoolRepository;
  private CollegeRepository collegeRepository;
  
  @Autowired
  public Query(SchoolRepository schoolRepository, CollegeRepository collegeRepository) {
    this.schoolRepository = schoolRepository;
    this.collegeRepository = collegeRepository;
  }

  public List<Object> searchResults(String val) {
    List<Object> results = new ArrayList<>();
    results.add(schoolRepository.find(val));
    results.add(collegeRepository.find(val));
    System.out.println(results); // getting output here

    return results; // but not returning here
  }
}