修正当模型定义了const UPDATED_AT = null;时批量更新导致的额外添加了更新时间导致的异常错误

Author: TestAdmin007

src/Batch.php

@@ -73,7 +73,7 @@ public function update(Model $table, array $values, string $index = null, bool $
             if ($table->usesTimestamps()) {
                 $updatedAtColumn = $table->getUpdatedAtColumn();
 
-                if (!isset($val[$updatedAtColumn])) {
+                if ($updatedAtColumn && !isset($val[$updatedAtColumn])) {
                     $val[$updatedAtColumn] = Carbon::now()->format($table->getDateFormat());
                 }
             }