Export to Disk Formatting

[JPK]

In Calibre 3.48 for Windows 10, I have formatted my export to disk as:

{authors} – {series}{series_index:0>2| | - }{title}

When there is a series in the filename, it exports the ebook files in this format:
Author Name - Series 03 - Title

Ebook files without a series, export in this format:
Author Name – Title
---------------------------------------------------------------------------------
I would like it to export ebook files with a series in the filename with brackets around the series in this format:
Author Name – [Series 03] - Title

But for ebook files without a series, to eliminate the series and the brackets in this format:
Author Name – Title

Can anyone give me string to do that?

[dunhill]

{authors} - {series}{series_index:0>2s| [ | ] }{title}