zotero-better-bibtex: Unicode replacement results in undefined mathsl command

Debug log ID

7W56UACL-refs-euc/6.7.140-7

What happened?

I was experimenting with the “Export unicode as plain-text latex commands option” using BibLaTeX.

I created a new entry in Zotero with the title “The 𝑘 is in unicode”. I then exported this item using Better BibLaTeX, which resulted in

@article{Unicode,
  title = {The {$\mathsl{k}$} Is in Unicode}
}

However, it doesn’t seem like mathsl is defined in any of the standard math packages (I’m using amsmath, amssymb) so compiling a document results in

! Undefined control sequence.
<recently read> \mathsl

It seems like mathsl is defined in the sfmath.sty package, but this forces all math symbols in the document to be sans serif.

Should the above be $k$ instead of $\mathsl{k}$? Or, did I simply choose the wrong unicode symbol (U+1D458) for what should be $k$?