Fixed issue with filters causing null ref when casting

BlazingCoffee/Client/Pages/Sales.razor

@@ -90,7 +90,7 @@
         {
             var state = Grid.GetState();
             // clear TransactionDate filters
-            state.FilterDescriptors = state.FilterDescriptors.Where(f => (f as FilterDescriptor).Member != "TransactionDate").ToList();
+            state.FilterDescriptors = state.FilterDescriptors.Where(f => (f as FilterDescriptor)?.Member != "TransactionDate").ToList();
             // assign new TransactionDate filters
             state.FilterDescriptors.Add(StartFilter());
             state.FilterDescriptors.Add(EndFilter());

BlazingCoffee/Server/Controllers/SalesController.cs

@@ -1,6 +1,7 @@
 using BlazingCoffee.Shared;
 using BlazingCoffee.Shared.Models;
 using Microsoft.AspNetCore.Mvc;
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Threading.Tasks;
@@ -24,7 +25,7 @@ namespace BlazingCoffee.Server.Controllers
         [HttpPost]
         public async Task<ActionResult<DataEnvelope<Sale>>> GetSales([FromBody]DataSourceRequest request)
         {
-            var result = await _context.Sales.ToDataSourceResultAsync(request);
+            DataSourceResult result = await _context.Sales.ToDataSourceResultAsync(request);
             var data = new DataEnvelope<Sale>
             {
                 CurrentPageData = result.Data.OfType<Sale>().ToList(),