"(null)" tooltip on some tab menu items

Environment/Versions

• GIMP version: 2.99.16
• Package: Flatpak and compiled from source
• Operating System: Linux

Description of the bug

(Previously discussed on irc and mentioned in #9578 (comment 1802156) , but couldn't find a dedicated bug, so filing a separate issue.)

The tooltip of multiple menu items, for example in the tab menu, is just (null) in 2.99.16.

Not present in stable release 2.10.36. In that version no tooltip is shown if there is no tooltip.

Null tooltip shown in 2.99.16

Reproduction

Is the bug reproducible? Always

Reproduction steps:

1. Hover pointer over e.g Close Tab or Detach Tab in the tab menu
2. The tooltip (null) is shown.

…

Expected result: No tooltip at all, or a tooltip actually containing some info.

Actual result: Only (null) is shown.