title: Cannot resolve ResponseEntity in SpringMVC using JpaRepository
body: <p>This is my Controller:</p>
  
  <pre><code>package com.hodor.booking.controller;
  
  import com.hodor.booking.jpa.domain.Vehicle;
  import com.hodor.booking.service.VehicleService;
  import com.wordnik.swagger.annotations.Api;
  import org.apache.commons.lang.time.DateUtils;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  import org.springframework.beans.factory.annotation.Autowired;
  import org.springframework.web.bind.annotation.*;
  
  import java.util.Date;
  import java.util.List;
  
  @RestController
  @RequestMapping("/api/v1/vehicles")
  @Api(value = "vehicles", description = "Vehicle resource endpoint")
  
  public class VehicleController {
  
      private static final Logger log = LoggerFactory.getLogger(VehicleController.class);
  
      @Autowired
      private VehicleService vehicleService;
  
      @RequestMapping(method = RequestMethod.GET)
      public List&lt;Vehicle&gt; index() {
          log.debug("Getting all vehicles");
          return vehicleService.findAll();
      }
  
      @RequestMapping(value="/save", method=RequestMethod.POST, consumes="application/json")
  
      @ResponseBody
      public Vehicle setVehicle(@RequestBody Vehicle vehicle) {
          log.debug("Inserting vehicle");
  
          if (vehicle.getLicensePlate() == null){
              return new ResponseEntity&lt;Void&gt;(HttpStatus.CONFLICT);
          }
  
          return vehicleService.saveVehicle(vehicle);
      }
  }
  </code></pre>
  
  <p>What I want to achieve in above If-Guard is that, in case the vehicle Object does not have the LicensePlate Member, send back an according HTTP Status Header CONFLICT or something. </p>
  
  <p>I am coming from a Node and Express background and I am used to set my header, send the response and be done with it. However in this case (JPA) it does not seem to work. Any ideas?</p>