Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exceptionエラーが発生しました。

やりたいこと

/home画面に、IndexMasterDtoを取得し、表示したいです。

######　エラー事象
下記のようなエラーが発生しました。解決方法が分からないです。
Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root cause

java.lang.NullPointerException: null
at xxxxxxxxx.controller.HomeController.home(HomeController.java:34) ~[classes/:na]

⇒HomeController.java（下記ソース参照）の
IndexMasterDto IndexMasterDto = idxMstService.findMasterByCategoryCode("C001", "1");
で、nullが発生します。

ソース

・IndexMaster.java

/**
 * エンティティクラス.
 * 
 */
@Entity
@IdClass(IndexMasterPk.class)
@Table(name = "indexMaster")
@Data
public class IndexMaster {

  @Id
  @Column(name = "category_code")
  private String categoryCode;

  @Column(name = "category_name")
  private String categoryName;

  @Id
  @Column(name = "code")
  private String masterCode;

  @Column(name = "name")
  private String masterName;

  @Column(name = "sort_order")
  private int sortOrder;

  @Column(name = "del_flg")
  private int delFlg;

  @Column(name = "setting1")
  private String masterSet1;

  @Column(name = "setting2")
  private String masterSet2;

  @Column(name = "setting3")
  private String masterSet3;

  @Column(name = "setting4")
  private String masterSet4;

  @Column(name = "setting5")
  private String masterSet5;

  public IndexMaster(String categoryCode, String categoryName, String masterCode, String masterName,
      int sortOrder, int delFlg, String masterSet1, String masterSet2, String masterSet3,
      String masterSet4, String masterSet5) {
    this.categoryCode = categoryCode;
    this.categoryName = categoryName;
    this.masterCode = masterCode;
    this.masterName = masterName;
    this.sortOrder = sortOrder;
    this.delFlg = delFlg;
    this.masterSet1 = masterSet1;
    this.masterSet2 = masterSet2;
    this.masterSet3 = masterSet3;
    this.masterSet4 = masterSet4;
    this.masterSet5 = masterSet5;
  }

  @Override
  public String toString() {
    return "indexMaster{" + "categoryCode=" + categoryCode + ", categoryName=" + categoryName
        + ", code=" + masterCode + ", name=" + masterName + '}';
  }

  public IndexMaster() {}

}

・IndexMasterPk.java

/**
 * エンティティ主キークラス.
 * 
 */
@Data
@Embeddable
public class IndexMasterPk implements Serializable {

  @Column(name = "category_code")
  private String categoryCode;

  @Column(name = "code")
  private String masterCode;

}

・IndexMasterDto.java

/**
 * DTOクラス.
 * 
 */
@Value
public class IndexMasterDto {
  private String categoryCode;
  private String categoryName;
  private String masterCode;
  private String masterName;
  private Long sortOrder;
  private Long delFlg;
  private String setting1;
  private String setting2;
  private String setting3;
  private String setting4;
  private String setting5;
}

・IndexMasterRepository.java

/**
 * レポジトリクラス.
 * 
 */
@Repository
public interface IndexMasterRepository extends JpaRepository<IndexMaster, String> {
  @Query("SELECT mst FROM IndexMaster mst WHERE mst.categoryCode = :categoryCode AND mst.masterCode = :masterCode")
  IndexMasterDto findMasterByCategoryCode(@Param("categoryCode") String categoryCode,
      @Param("masterCode") String masterCode);
}

・IndexMasterService.java

/**
 * サービスクラス.
 * 
 */
public interface IndexMasterService {

  IndexMasterDto findMasterByCategoryCode(String categoryCode, String masterCode);

}

・IndexMasterServiceImpl.java

/**
 * クラス.
 * 
 */
@Service
public class IndexMasterServiceImpl implements IndexMasterService {

  @Autowired
  private IndexMasterRepository repository;

  /**
   * 取得.
   *
   * @param categoryCode カテゴリコード
   * @param masterCode コード
   * @return カテゴリ内容
   */
  @Cacheable("IndexMaster")
  @Override
  public IndexMasterDto findMasterByCategoryCode(String categoryCode, String masterCode) {
    return repository.findMasterByCategoryCode(categoryCode, masterCode);
  }

}

・HomeController.java

/**
 * ホーム画面コントローラクラス.
 * 
 */
@Controller
@Slf4j
public class HomeController {

  @Autowired
  private IndexMasterService idxMstService;

  @GetMapping("/home")
  public String home(Model model) {
    IndexMasterDto IndexMasterDto = idxMstService.findMasterByCategoryCode("C001", "1");
    model.addAttribute("lst", IndexMasterDto);
    return "home";
  }

}

参考にデータは、
INSERT INTO indexMaster(category_code,category_name,code,name,sort_order,del_flg,setting1,setting2,setting3,setting4,setting5) VALUES ('C001','グループ種別','1','パブリック',10,0,'set1','set2','set3','set4','set5');