如何在没有datafetcher的情况下为graphql-java配置REST控制器？

GraphQLSchema schema = new GraphQLSchema.Builder()
    .query(new GraphQLObjectType.Builder()
        .name("Query")
        .field(newFieldDefinition()
            .name("hello")
            .type(Scalars.GraphQLString)
            .dataFetcher(environment -> "Hello, GraphQL!")
            .build())
        .build())
    .build();

@RestController
@RequestMapping("/api")
public class GraphQLController {

    private final GraphQLSchema schema;

    public GraphQLController(GraphQLSchema schema) {
        this.schema = schema;
    }

    @PostMapping("/graphql")
    public ResponseEntity<Object> executeGraphQL(@RequestBody Map<String, Object> request) {
        ExecutionResult executionResult = new GraphQL(schema).execute(request.get("query").toString());
        return ResponseEntity.ok(executionResult.toSpecification());
    }
}