如何解决“从角度发布数据收集时出现空值问题”？

Question

我正在尝试在数组中添加数据。添加后，一旦用户单击“提交”，数据就会转换为JSON对象并调用asp.net核心服务。我传递到后端的数据为空

<mat-form-field>
<mat-accordion class="example-headers-align" *ngIf="concatArray">
  <mat-expansion-panel *ngFor="let item of concatArray" hideToggle>
    <mat-expansion-panel-header>
      <mat-panel-title>
        {{item[0].key}}
      </mat-panel-title>
      <mat-panel-description>
        Need To Improve?
        <mat-icon matSuffix>sentiment_very_satisfied</mat-icon>
      </mat-panel-description>
    </mat-expansion-panel-header>
    <mat-label>
      <mat-checkbox *ngFor="let dish of item[0].value" (click)="onItemClicked(dish)"  class="example-margin"
        [labelPosition]="labelPosition" [disabled]="disabled">
        {{dish.dishName}}
      </mat-checkbox>
    </mat-label>
  </mat-expansion-panel>
  <mat-action-row>
    <button mat-button color="warm" (click)="onSubmit()">Submit</button>
  </mat-action-row>
</mat-accordion>
</mat-form-field>

export class FeedbackComponent implements OnInit {
  panelOpenState = true;
  public dishMenu: Dishes[];
  public dishes: Dishes[] = [];
  checked = false;
  concatArray = [];
  indeterminate = false;
  labelPosition = 'after';
  isSelected = false;
  disabled = false;
  commentList: string[] = ['Extra Cooked', 'Oily', 'Not Cooked', 'Taste', 'Others'];

  ngOnInit(): void {
    this.dishService.getDishes().subscribe(result => {
      this.dishMenu = result.dishes;
      this.concatArray = _.chain(this.dishMenu)
        .groupBy(x => x.type)
        .map((item, description) => [{ key: description, value: item }])
        .value();
      console.log(this.concatArray);
    });
  }

  constructor(@Inject(MAT_BOTTOM_SHEET_DATA) public data: any,
    // tslint:disable-next-line:align
    private dishService: DishMenuService, public dialog: MatDialog, private commonService: CommonService) {
  }
  onItemClicked(dish: Dishes) {
    console.log(dish);
    const dishFeedback = new Dishes(dish);
    dishFeedback.dishRating = this.data.rating;
    dishFeedback.tenantId = this.data.userId;
    this.dishes.push(dishFeedback);
    console.log(this.dishes);
  }

  onSubmit() {
    console.log(this.dishes);
    this.dishService.submitDishFeedback(this.dishes).subscribe(result => {
      if (result) {
        const validate = new ValidationModel();
        validate.validationMessage = 'Thank you!!';
        validate.validationType = ValidationType.success;
        this.dialog.closeAll();
        this.commonService.openSnackBar(validate);
      }
    });
  }
}
export class DishMenuService {

  constructor(private urlEndPoint: YNGBUrlEndPoints, private httpClient: HttpClient
  ) {

  }

  submitDishFeedback(dish: Dishes[]) {
    const dishFeedBackUrl = this.urlEndPoint.getDishFeedbackUrl();
    var dishes=JSON.stringify(dish);
    return this.httpClient.post(dishFeedBackUrl, {"dishModel":dishes})
      .pipe(map(result => result));
  }
}

  public class DishModel
    {
        public List<DishFeedbackModel> Dishes { get; set; }
    }
 public class DishMain
    {
        public string DishId { get; set; }
        public string DishName { get; set; }
        public string Type { get; set; }
    }
   public class DishFeedbackModel : DishMain
    {
        public int DishRating { get; set; }
        public string Comment { get; set; }
        public string TenantId { get; set; }
    }

    [Route("api/[controller]")]
    [ApiController]
    public class DishFeedbackController : ControllerBase
    {
        private readonly IDishFeedbackRepository _dishFeedbackRepository;

        public DishFeedbackController(IDishFeedbackRepository dishFeedbackRepository)
        {
            _dishFeedbackRepository = dishFeedbackRepository;
        }
        [HttpPost]
        public async Task<bool> Post([FromBody]DishModel dishModel)
        {
            if (dishModel == null)
            {
                throw new NullReferenceException("Value of DishModel cannot be null");
            }
            var result = await _dishFeedbackRepository.AddDishFeedback(dishModel);
            return result;
        }
    }

我从前端提交的数据为空，我需要将其与列表菜映射