FYI: a patch to prevent showing this blank "ghost" icon, i.e. the upstream fix for https://bugs.kde.org/show_bug.cgi?id=358719, has been added to our plasma5-workspace package now too. And according to https://github.com/fcitx/fcitx/issues/241 the issue in fcitx (that it creates this icon in the first place) should be fixed in master.