What is the bug or the crash?

When labelling contains round($length,2) then sld export gives error. QGIS version is 3.44.3

Steps to reproduce the issue

1. Double click on a line layer and open "Properties" panel.
2. Go to Labelling tab, and write "round($length,2)" as expression
3. Save this style as sld file.

Versions

QGIS 3.44.3

Supported QGIS version

• I'm running a supported QGIS version according to the roadmap.

New profile

• I tried with a new QGIS profile

Additional context

No response