这是我的服务课

package com.example.demo.service;
import com.example.demo.dto.Invoicedto;
import com.example.demo.model.Item;
import com.example.demo.repository.ItemRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import java.util.List;
@Service
public class InvoiceService implements InvoiceServiceInterface {
    @Autowired
    private ItemRepository itemRepository;
    public void createInvoice(Invoicedto invoiceDto) {
        try {
            List<Item> itemList = this.itemRepository.findAll();
            for (Item item : itemList) {
                System.out.println(item.getId());
            }
        } catch (Exception e) {
            System.out.println("Exception occurred " + e.getMessage());
        }
    }
}

这是我的仓库

package com.example.demo.repository;
import com.example.demo.model.Item;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Modifying;
import org.springframework.data.jpa.repository.Query;
import org.springframework.stereotype.Repository;
import org.springframework.transaction.annotation.Transactional;
import java.util.List;
@Repository
public interface ItemRepository   extends JpaRepository<Item, Long> {
    List<Item> findAll();
    @Modifying
    @Query("DELETE Item c WHERE c.id = ?1")
    void deleteById(long id); 
}

虽然我添加了必要的注解，但这总是给予
出现异常无法调用“com.example.demo.repository.itemRepository.findAll（）”，因为“此.itemRepository”为空
为什么会发生这种情况，解决办法是什么？