Check if TextProperty is set when attempting to use it for filter

Radzen.Blazor/DropDownBase.cs

@@ -732,7 +732,9 @@ protected virtual async System.Threading.Tasks.Task HandleKeyPress(Microsoft.Asp
             }
             else
             {
-                var filteredItems = Query.Where(TextProperty, args.Key, StringFilterOperator.StartsWith, FilterCaseSensitivity.CaseInsensitive)
+                var filteredItems = (!string.IsNullOrEmpty(TextProperty) ?
+                    Query.Where(TextProperty, args.Key, StringFilterOperator.StartsWith, FilterCaseSensitivity.CaseInsensitive) :
+                    Query)
                     .Cast<object>()
                     .ToList();