Object Must implement IConvertible Declined - Won't fix

An exception of type 'System.InvalidCastException' occurred in System.Private.CoreLib.dll but was not handled in user code

Object must implement IConvertible."

on the bold line of following code when trying to filter (on a EJ2 datagrid)

        [HttpPost]
        public ActionResult PostProduct([FromBody] DataManagerRequest dm)
        {

            var products = _context.Products.AsQueryable();

            DataOperations operation = new DataOperations();

            if (dm.Where != null && dm.Where.Count > 0) // Filtering
            {
                products = operation.PerformFiltering(products, dm.Where, dm.Where[0].Operator);  <<<<<<<<<<<<<<<<< THIS LINE GIVES THE ERROR
            }

            System.Text.Json.JsonSerializerOptions a = new System.Text.Json.JsonSerializerOptions
            {
                PropertyNamingPolicy = null,
            };

            return dm.RequiresCounts ? new JsonResult(new { result = products, count = products.Count() }, a) : new JsonResult(products, a);


        }

any ideas why I get this?