Summary says by itself.
The same option is disabled in context menu from "Trash" in Dolphin sidebar
when trash is empty.
Git commit 7e98c5d737eb953c8a2692b7eeae1b4cb0f32e5f by Kai Uwe Broulik.
Committed on 05/04/2018 at 12:03.
Pushed by broulik into branch 'Plasma/5.12'.
[Folder View] Update "Empty Trash" enabled state for files inside Trash and links to Trash
Previously this was only done for files inside Trash. Now also the context menu of a Trash link has correct state.
Differential Revision: https://phabricator.kde.org/D11944
M +8 -2 containments/desktop/plugins/folder/foldermodel.cpp
M +1 -0 containments/desktop/plugins/folder/foldermodel.h