API软件中的对象引用错误解决

Question

我正在用C＃创建一个API，但遇到了无法解释的错误。

"responseStatus": {
  "errorCode": "NullReferenceException",
  "message": "Object reference not set to an instance of an object.",
  "stackTrace": null,
  "errors": [],
  "meta": null
}

所有其他API调用均以相同的方式工作，但这仅会产生错误。

public class PartnerService : BaseService
{
  public IPartnerRepository PartnerRepository { get; set; }
  [RequiresAnyRole(Roles.superadmin, Roles.admin)]
  public async Task<PartnerListResponse> Get(PartnerListRequest request)
  {
    var items = await PartnerRepository.GetAllAsync(); // this is the error line
    return new PartnerListResponse
    {
      Items = items
    };
  }
}

IpartnerRepository

using System;
using System.Collections.Generic;
using System.Text;
using DTO = Ringdesk.Api.ServiceModel.DTO;
namespace Ringdesk.Api.ServiceModel.Interfaces
{
  public interface IPartnerRepository : IDtoRepository<DTO.Partner, 
  DTO.PartnerForInsert, DTO.PartnerForUpdate>
  {
  }
}

合作伙伴模型

[Route("/partners", Verbs = "GET", Summary = "Retrieve a list of partners")]
public class PartnerListRequest : IReturn<PartnerListResponse>
{

}

public class PartnerListResponse : ResponseBase
{
   public List<DTO.Partner> Items { get; set; }
}

为什么会出现此错误？