LSP: Recurring soft assert

Steps to reproduce:

• create a widget app from template
• build it
• open mainwindow.cpp
• place cursor onto setupUi() call, hit F2
  • you should be now inside the generated ui_mainwindow.h
• close the file

QC prints soft assert:
SOFT ASSERT [11:35:59.812]: "shadowIt.value().second.isEmpty()" in /home/qt/work/build/qt-creator/src/plugins/languageclient/client.cpp:807