On line 183 of qwindows11style.cpp, styleOption is set (https://code.qt.io/cgit/qt/qtbase.git/tree/src/plugins/styles/modernwindows/qwindows11style.cpp). However there is no check that it's not NULL before it's used, which is leading to a crash in my application when drawing a slider.

I don't have a MWE but hopefully this is obvious enough to be fixed without a MWE. 

There may also be improper uses on lines 212-213, 410, 412, and 415. There are places in the same file where styleObject is checked, on lines 696, 736, and 860.