framework/db/Migration.php
public function down()
    {
        $transaction = $this->db->beginTransaction();
        try {
            if ($this->safeDown() === false) {
                $transaction->rollBack();
                return false;
            }
            $transaction->commit();
        } catch (\Exception $e) {
            $this->printException($e);
            $transaction->rollBack();
            return false;
        } catch (\Throwable $e) {
            $this->printException($e);
            $transaction->rollBack();
            return false;
        }

        return null;
    }
public function down()
    {
        $transaction = $this->db->beginTransaction();
        try {
            if ($this->safeDown() === false) {
                $transaction->rollBack();
                return false;
            }
            $transaction->commit();
        } catch (\Exception $e) {
            $this->printException($e);
            $transaction->rollBack();
            return false;
        } catch (\Throwable $e) {
            $this->printException($e);
            $transaction->rollBack();
            return false;
        }

        return null;
    }
This method contains the logic to be executed when removing this migration.
The default implementation throws an exception indicating the migration cannot be removed.
Child classes may override this method if the corresponding migrations can be removed.
@return bool return a false value to indicate the migration fails
and should not proceed further. All other return values mean the migration succeeds.