blazor.web.js:1 crit: Microsoft.AspNetCore.Components.WebAssembly.Rendering.WebAssemblyRenderer[100]
      Unhandled exception rendering component: Object reference not set to an instance of an object.
System.NullReferenceException: Object reference not set to an instance of an object.
   at Telerik.Blazor.Components.Common.ColumnMenu.ColumnMenu`1.<OnColumnChooserColumnVisibilityChange>d__188[[BlazorRepl.UserComponents.__Main.FlatModel, BlazorRepl.UserComponents, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null]].MoveNext()
   at Telerik.Blazor.Components.Common.ColumnMenu.ColumnMenuChooser.OnApplyClick()
   at Microsoft.AspNetCore.Components.ComponentBase.CallStateHasChangedOnAsyncCompletion(Task task)
   at Microsoft.AspNetCore.Components.RenderTree.Renderer.GetErrorHandledTask(Task taskToHandle, ComponentState owningComponentState)

public class TreeNodeViewModel
{
    public string NodeName { get; set; }
    public IEnumerable<TreeNodeViewModel> Children { get; set; }
    public bool Expanded { get; set; }
    public string Color { get; set; }
    public string IconClass { get; set; }
}

<style>
    /*should work but does not*/
    .high-zindex {
        z-index: 124;/*note how this is higher than the z-index of the div element, and is higher than the default z-index of the component*/
    }

    /*workaround*/
    .k-animation-container {
        z-index: 15000;
    }
</style>

<div style="position: absolute; z-index: 123; width: 600px; height: 200px; background: yellow;">
    <TelerikMultiSelect Data="@Countries"
                        @bind-Value="@Values"
                        Placeholder="Enter Balkan country, e.g., Bulgaria"
                        ClearButton="true" AutoClose="false"
                        PopupClass="high-zindex">
    </TelerikMultiSelect>
</div>

@code {
    List<string> Countries { get; set; } = new List<string>();
    List<string> Values { get; set; } = new List<string>();

    protected override void OnInitialized()
    {
        Countries.Add("Albania");
        Countries.Add("Bosnia & Herzegovina");
        Countries.Add("Bulgaria");
        Countries.Add("Croatia");
        Countries.Add("Kosovo");
        Countries.Add("North Macedonia");
        Countries.Add("Montenegro");
        Countries.Add("Serbia");
        Countries.Add("Slovenia");

        base.OnInitialized();
    }
}

@page "/districts"
@using MVC.Services
@using MVC.Models
@using System.ComponentModel.DataAnnotations
@inject IDistrictService DistrictService
<h3>Districts</h3>
<TelerikGrid Data="@district" Sortable="true" EditMode="@GridEditMode.Incell"
             Height="500px"
             Pageable="true" PageSize=@PageSize
             OnUpdate=@UpdateItem OnDelete=@DeleteItem OnCreate=@CreateItem OnCancel="@OnCancelHandler">
    <GridToolBar>
        <GridCommandButton Command="Add" Icon="add">Add District</GridCommandButton>
    </GridToolBar>
    <GridColumns>
        <GridColumn Field="@(nameof(District.Id))" Editable="false" />
        <GridColumn Field="@(nameof(District.Description))" Title="Description" />
        <GridColumn Field="@(nameof(District.EnableApprovalWorkflow))" Title="Enable Approval Workflow" />
        <GridCommandColumn>
            <GridCommandButton Command="Delete" Icon="delete">Delete</GridCommandButton>
        </GridCommandColumn>
    </GridColumns>
</TelerikGrid>
@code {
    int PageSize = 15;
    IEnumerable<District> district;

    protected override async Task OnInitializedAsync()
    {
        await GetGridData();
    }
    async Task GetGridData()
    {
        district = await DistrictService.DistrictList();
    }
    async Task CreateItem(GridCommandEventArgs args)
    {
        District item = (District)args.Item;
        await DistrictService.DistrictInsert(item);
        await GetGridData();
    }

    void OnCancelHandler(GridCommandEventArgs args)
    {
        District item = (District)args.Item;
    }

    async Task DeleteItem(GridCommandEventArgs args)
    {
        District item = (District)args.Item;
        await DistrictService.DistrictDelete(item.Id);
        await GetGridData();
    }

    async Task UpdateItem(GridCommandEventArgs args)
    {
        District item = (District)args.Item;
        await DistrictService.DistrictUpdate(item);
        await GetGridData();
    }
}

using Dapper;
using Microsoft.Data.SqlClient;
using MVC.Models;
using System;
using System.Collections.Generic;
using System.Data;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace MVC.Services
{
    public class DistrictService : IDistrictService
    {
        private readonly SqlConnectionConfiguration _configuration;
        public DistrictService(SqlConnectionConfiguration configuration)
        {
            _configuration = configuration;
        }
        public async Task<bool> DistrictInsert(District district)
        {
            using (var conn = new SqlConnection(_configuration.Value))
            {
                var parameters = new DynamicParameters();
                parameters.Add("Description", district.Description, DbType.String);
                parameters.Add("EnableApprovalWorkflow", district.EnableApprovalWorkflow, DbType.Boolean);
                await conn.ExecuteAsync("spLookupDistrict_Insert", parameters, commandType: CommandType.StoredProcedure);
            }
            return true;
        }
        public async Task<IEnumerable<District>> DistrictList()
        {
            IEnumerable<District> districts;
            using (var conn = new SqlConnection(_configuration.Value))
            {
                districts = await conn.QueryAsync<District>("spLookupDistrict_List", commandType: CommandType.StoredProcedure);
            }
            return districts;
        }
        public async Task<IEnumerable<District>> DistrictSearch(string @Param)
        {
            var parameters = new DynamicParameters();
            parameters.Add("@Param", Param, DbType.String);
            IEnumerable<District> districts;
            using (var conn = new SqlConnection(_configuration.Value))
            {
                districts = await conn.QueryAsync<District>("spLookupDistrict_Search", parameters, commandType: CommandType.StoredProcedure);
            }
            return districts;
        }
        public async Task<District> District_GetOne(int @Id)
        {
            District district = new District();
            var parameters = new DynamicParameters();
            parameters.Add("@Id", Id, DbType.Int32);
            using (var conn = new SqlConnection(_configuration.Value))
            {
                district = await conn.QueryFirstOrDefaultAsync<District>("spLookupDistrict_GetOne", parameters, commandType: CommandType.StoredProcedure);
            }
            return district;
        }
        public async Task<bool> DistrictUpdate(District district)
        {
            using (var conn = new SqlConnection(_configuration.Value))
            {
                var parameters = new DynamicParameters();
                parameters.Add("Id", district.Id, DbType.Int32);

                parameters.Add("Description", district.Description, DbType.String);
                parameters.Add("EnableApprovalWorkflow", district.EnableApprovalWorkflow, DbType.Boolean);

                await conn.ExecuteAsync("spLookupDistrict_Update", parameters, commandType: CommandType.StoredProcedure);
            }
            return true;
        }
        public async Task<bool> DistrictDelete(int Id)
        {
            var parameters = new DynamicParameters();
            parameters.Add("@Id", Id, DbType.Int32);
            using (var conn = new SqlConnection(_configuration.Value))
            {
                await conn.ExecuteAsync("spLookupDistrict_Delete", parameters, commandType: CommandType.StoredProcedure);
            }
            return true;
        }
    }
}

<TelerikWindow @bind-Visible="ShowAdd" Modal="true" Class="NewRequest">
    <WindowTitle>Add Applications</WindowTitle>
    <WindowContent>
        <div style="position: relative; width: 90vw; max-width: 400px; display: grid; ">
            <span style="font-size: medium">@thisEmployee.EmpNickName</span>
            <div style="align-content: center; padding: 5px; width: 100%; display:flex; justify-content: center; align-items: center; border: inset">
                <div style="padding: 1px "><label for="ckDev">Dev</label><TelerikCheckBox Id="ckDev" @bind-Value="@thisEmployee.Developer" /></div>
                <div style="padding: 1px "><label for="ckSales">Sales</label><TelerikCheckBox Id="ckSales" @bind-Value="@thisEmployee.Salesman" /></div>
                <div style="padding: 1px "><label for="ckEng">Eng</label><TelerikCheckBox Id="ckEng" @bind-Value="@thisEmployee.Engineer" /></div>
                <div style="padding: 1px "><label for="ckPE">PE</label><TelerikCheckBox Id="ckPE" @bind-Value="@thisEmployee.LeadEng" /></div>
                <div style="padding: 1px "><label for="ckPM">PM</label><TelerikCheckBox Id="ckPM" @bind-Value="@thisEmployee.PM" /></div>
                <div style="padding: 1px "><label for="ckPurch">Purch</label><TelerikCheckBox Id="ckPurch" @bind-Value="@thisEmployee.Purchasing" /></div>
                <div style="padding: 1px "><label for="ckSF">Shop</label><TelerikCheckBox Id="ckSF" @bind-Value="@thisEmployee.ShopFore" /></div>
                <div style="padding: 1px "><label for="ckFS">Super</label><TelerikCheckBox Id="ckFS" @bind-Value="@thisEmployee.FieldSuper" /></div>
            </div><br />
            <div style="font-size:smaller">
                <TelerikGrid Data="@allApps" Height="50vh" FilterMode="@GridFilterMode.FilterMenu" FilterMenuType="@FilterMenuType.CheckBoxList">
                    <GridColumns>
                        <GridColumn Field="MenuCategoryTitle" Title="Category" />
                        <GridColumn Field="MenuCategoryID" Width="0" />
                        <GridColumn Width="3em">
                            <Template>
                                <div style="float:left; cursor:pointer; color: forestgreen; padding-right: 8px" title="Add Category" @onclick="@((args) => AddCategory((context as Index_Menu).MenuCategoryID))"><ic class="fad fa-plus-square" /></div>
                            </Template>
                        </GridColumn>
                        <GridColumn Field="MenuItemID" Width="0" />
                        <GridColumn Field="MenuItemTitle" Title="App" />
                        <GridColumn Width="3em">
                            <Template>
                                @if ((context as Index_Menu).MIAssigned == false)
                                {
                                    <div style="float:left; cursor:pointer; color: forestgreen; padding-right: 8px" title="Add App" @onclick="@((args) => AddItem((context as Index_Menu).MenuItemID))"><ic class="fad fa-plus-square" /></div>
                                }
                                else
                                {
                                    <div style="float:left; cursor:pointer; color: red; padding-right: 8px" title="Delete App" @onclick="@((args) => DeleteApp((context as Index_Menu).MenuItemID))"><ic class="fad fa-trash-alt" /></div>
                                }
                            </Template>
                        </GridColumn>
                    </GridColumns>
                </TelerikGrid>
            </div>
            <div style="align-content:center; padding:5px; width: 100%; display: flex;  justify-content: center;  align-items: center;  ">
                <TelerikButton OnClick="@CancelWindow">CLOSE</TelerikButton>
            </div>
        </div>
    </WindowContent>
</TelerikWindow>