Proposed changes

1. this pr is used to fix the wrong result of array_join function.
2. before the change, the array_join function will return wrong result.
   MySQL [example_db]> select array_join(["", "1", "2"], '');
   +--------------------------------------+
   | array_join(ARRAY('', '1', '2'), '') |
   +--------------------------------------+
   | 1_2 |
   +--------------------------------------+
   3.after the change, the array_join function will return correct result.
   MySQL [example_db]> select array_join(["", "1", "2"], '');
   +--------------------------------------+
   | array_join(ARRAY('', '1', '2'), '') |
   +--------------------------------------+
   | _1_2 |
   +--------------------------------------+

Issue Number: #7570

Problem summary

Describe your changes.

Checklist(Required)

1. Does it affect the original behavior:
   • Yes
   • No
   • I don't know
2. Has unit tests been added:
   • Yes
   • No
   • No Need
3. Has document been added or modified:
   • Yes
   • No
   • No Need
4. Does it need to update dependencies:
   • Yes
   • No
5. Are there any changes that cannot be rolled back:
   • Yes (If Yes, please explain WHY)
   • No

Further comments

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