return null value for empty/null strings

Author: mark-git07

src/Jobs/DataTableExportJob.php

@@ -160,7 +160,7 @@ public function handle()
                         $format = $column->exportFormat ?? $defaultDateFormat;
                         break;
                     case $this->wantsNumeric($column):
-                        $cellValue = floatval($value);
+                        $cellValue = ( trim($value) == '' || is_null($value) ) ? null : floatval($value);
                         $format = $column->exportFormat;
                         break;
                     case CellTypeHelper::isDateTimeOrDateInterval($value):