Got this error when trying to open the Journal in a system (actually happened twice in two different systems), when trying to record the location of a derelict. Literally the first time I've had an issue across multiple runs, so figured I'd report it.
Spoiler
2184536 [Thread-3] ERROR com.fs.starfarer.combat.CombatMain - java.lang.IllegalStateException: shipVariant must not be null
java.lang.IllegalStateException: shipVariant must not be null
at fleetjour.scripts.panel.Common.getHullClassOfDerelict(Common.kt:41)
at fleetjour.scripts.objects.SelectableEntity.createContainer(SelectableEntity.kt:31)
at fleetjour.scripts.panel.EntitySelectorPanel.createEntitiesSelector(EntitySelectorPanel.kt:127)
at fleetjour.scripts.panel.WriterPanelAssembly.renderEntitiesContainer(WriterPanelAssembly.kt:180)
at fleetjour.scripts.panel.WriterPanelAssembly.assemblePanel(WriterPanelAssembly.kt:92)
at fleetjour.scripts.EntryWriter.createLargeDescription(EntryWriter.kt:94)
Thank you for the bugreport! Need to put some additional checks in the method, will hopefully post a hotfix in a few minutes, since the issue is fairly critical. Please hold onto that save and that system, there might be some specific config of ship derelict data (perhaps caused by mods), which needs testing.
Edit: uploaded an altered version, you might want to try that system once again. I'm not normally in the habit of posting unfinished work, but this one contains currently-not-working entries management feature - don't mind it, save-compatible.
Should the error still persist, I will need more specifics (derelict ship class, modlist, etc).