I have a service which calls controller, which has cacheservice to send response data as location list based on customerId. As shown in below code, I am using it for paging. But I get null value at first response and then when I focus out and focus back to dropdown, I get the response. It would be better to understand based on code.

IndexFormPage.razor

<FormItem>
    <Template>
        <label for="tkbxLocationName" class="k-label k-form-label">@($"{locationFieldName} {MOM.Alias.Common.DTO.Name}")</label>
        <div class="d-flex">
            <TelerikComboBox TItem="@LocationDropdownDTO" TValue="@(int)"
                             ScrollMode="@DropDownScrollMode.Virtual"
                             OnRead="@GetLocationItems"
                             ItemHeight="60"
                             PageSize="20"
                             Size="@size" Rounded="@size"
                             Placeholder="Select Location Name" Id="tkbxLocationName"
                             TextField="@(nameof(LocationDropdownDTO.Name))"
                             ValueField="@(nameof(LocationDropdownDTO.Id))"
                             @bind-Value="@Dto.LocationId"
                             OnChange="@OnLocationChange"
                             ValueMapper="(val) => HandlelocationValueMapper(val)"
                             @ref="@refLocationDropDown"
                             AllowCustom="false"
                             Width="@TaskCategoryFieldUpWidth"
                             Filterable="true" Class="condition-field-width"
                             FilterOperator="@((Telerik.Blazor.StringFilterOperator)ReusableFilterOperator)"
                             DebounceDelay="@MOM.UI.Client.Constants.Common.SearchBoxDebounceDelay">
                <NoDataTemplate>
                    <MOM.UI.Client.Components.NoContent></MOM.UI.Client.Components.NoContent>
                </NoDataTemplate>
                <ComboBoxSettings>
                    <ComboBoxPopupSettings Height="200px" />
                </ComboBoxSettings>                
            </TelerikComboBox>            
            <TelerikValidationTooltip For="@(() => @Dto.LocationId)" TargetSelector="#tkbxLocationName" />
        </div>
    </Template>
</FormItem>


@code{
async Task GetLocationItems(ReadEventArgs args)
{
    DataSourceRequest newRequest = new DataSourceRequest()
    {
        Filters = new List<IFilterDescriptor>()
    };

    if (RecordLoading)
    {

        args.Request.Filters.Clear();
        newRequest.Filters.Add(new FilterDescriptor
        {
            Member = nameof(LocationDTO.Id),
            Operator = Telerik.DataSource.FilterOperator.IsEqualTo,
            MemberType = typeof(int),
            Value = Dto.LocationId
        });
    }
    else
    {
        newRequest = GenerateLocationCustomFilterRequest(args.Request);
        if (Dto.CustomerId > 0)
        {
            newRequest.Filters.Add(new FilterDescriptor
            {
                Member = nameof(LocationDTO.CustomerId),
                Operator = Telerik.DataSource.FilterOperator.IsEqualTo,
                MemberType = typeof(int),
                Value = Dto.CustomerId
            });
            newRequest.Skip = 0;
            //newRequest.PageSize = 100;
        }
    }
    if (RanderFromCustomer && CustomerId > 0)
    {
        newRequest.Filters.Add(new FilterDescriptor
        {
            Member = nameof(LocationDTO.CustomerId),
            Operator = Telerik.DataSource.FilterOperator.IsEqualTo,
            MemberType = typeof(int),
            Value = CustomerId
        });
    }

    if (RanderFromLocation && LocationId > 0)
    {
        newRequest.Filters.Add(new FilterDescriptor
        {
            Member = nameof(LocationDTO.Id),
            Operator = Telerik.DataSource.FilterOperator.IsEqualTo,
            MemberType = typeof(int),
            Value = LocationId
        });
    }
    var result = await _locationservice.GetAllForDropDownWithPaging(newRequest, Dto.BranchId);
    //newRequest.PageSize = result.Data.TotalItemCount;
    args.Data = result?.Data?.CurrentPageData;
    args.Total = result.Data.TotalItemCount;
}
}

LocationService.cs

public async Task<Response<DataEnvelope<LocationDropdownDTO>>> GetAllForDropDownWithPaging(DataSourceRequest gridRequest, byte branchId)
{
    try
    {
        HttpResponseMessage response = await _service.httpClient.PostAsync($"{API.Location}/{API.GetAllForDropDownWithPaging}/{branchId}", new StringContent(JsonConvert.SerializeObject(gridRequest), Encoding.UTF8, API.MediaType));
        return await response.Content.ReadFromJsonAsync<Response<DataEnvelope<LocationDropdownDTO>>>();
    }
    catch (System.Exception ex)
    {

        throw ex;
    }
}

LocationController.cs

public async Task<ActionResult<DataEnvelope<LocationDropdownDTO>>> GetAllForDropDownWithPaging([FromBody] DataSourceRequest gridRequest, byte branchId)
{
    Response<List<LocationDropdownDTO>> result;
    DataEnvelope<LocationDropdownDTO> dataToReturn;
    try
    {
        result = _cacheService.GetData<Response<List<LocationDropdownDTO>>>(CacheConstant.AllLocationCache);
        if (result == null)
        {
            result = await _service.GetAllForDropDown();
            DateTimeOffset expirationTime = DateTimeOffset.Now.AddMinutes(CacheConstant.CacheExpirationTime);
            _ = _cacheService.SetData<Response<List<LocationDropdownDTO>>>(CacheConstant.AllLocationCache, result, expirationTime);
        }
        IQueryable<LocationDropdownDTO> queriableData = result.Data.
             Where(x => x.BranchId == branchId).AsQueryable();

        DataSourceResult processedData = await queriableData.ToDataSourceResultAsync(gridRequest);

        dataToReturn = new DataEnvelope<LocationDropdownDTO>
        {
            CurrentPageData = processedData.Data.Cast<LocationDropdownDTO>().ToList(),
            TotalItemCount = processedData.Total
        };
    }
    catch (Exception ex)
    {

        throw ex;
    }
    return Ok(new Response<DataEnvelope<LocationDropdownDTO>> { Data = dataToReturn, Message = "SUCCESS" });

}

Please help me on this.