Function Help for Custom Tag

[phred]

I'm trying to create a custom tag to display featured artists. And to not display if there aren't any. This is based on <Artists: Guest> and what I'm trying to do is if the track has no guest artist(s), then don't show it, otherwise display "Featured: <Artists: Guest>. Seems simple enough, but the function seems to be choking at the first <Artists:Guest>.
This is what I think should work:

Code

$IsNull(<Artists:Guest>,,Featuring: <Artists:Guest>

The error message I'm getting is:
FAIL @ "ists:Guest>,,Featuring: <Artists:Guest>"

Why is it cutting off "Art"  from the first tag?

FWIW, -this- works: Featuring: <Artists: Guest> when I use it in Track Details, but if there are no guest artists is shows 'Featuring:'.

Thanks.
 

[psychoadept]

Is that a direct copy from your tag? The $IsNull is missing a close parenthesis.

[phred]

Is that a direct copy from your tag? The $IsNull is missing a close parenthesis.

<sigh> Yes, it was a direct copy. But even adding the close parenthesis, it still throws the same FAIL error.
For example, this works:

Code

$IsNull(<Playlist>,None,<Playlist>)

While this does not:

Code

$IsNull(<Artists:Guest>,,Featuring: <Artists:Guest>)

[hiccup]

There is a space missing; it should be <Artists: Guest>

(if you use the field selector drop-down menu you can check the available tags and their exact names)

[phred]

There is a space missing; it should be <Artists: Guest>
(if you use the field selector drop-down menu you can check the available tags and their exact names)

All along I was figuring either syntax or typo. I didn't suspect both. I know about the selector, and thought I had used it, but apparently not.

Thanks to psychoadept and you, problem solved.