Cannot return plain string from @BasePathAwareController method

It is not possible to return a plain String from a rest controller when it is annotated with @BasePathAwareController.   

This normal controller works (but in this controller I for example couldn't inject PersistentEntityResourceAssembler)

@RestController
@RequestMapping("${spring.data.rest.base-path}")   // to expose under correct basepath
public class UserRestController {
  @RequestMapping("/getStringExample")   
  public @ResponseBody String getStringExample() {
    return "Some dummy String"
  }
}

But this does not work:

@BasePathAwareController
public class UserRestController {
  @RequestMapping("/getStringExample")   
  public @ResponseBody String getStringExample() {
    return "Some dummy String"
  }
}

This returns a quoted string.   Adding produces = "text/plain" also doesn't help. It doesn't work no matter if you use @ResponseBody or not.

Even when you return a ResponseEntity.ok("Some dummy String");   the result will still be quoted in the final response.

How can I return a plain String (e.g. a token) from a @BasePathAwareController?