When passing too many names to QMetaMethodBuilder::setParameterNames():

    mmb = builder.addSlot("add(int)");
    mmb.setParameterNames({"", "i"}); 

a hard-to-comprehend assert occurs in 6.11:

ASSERT: "!buf || dataIndex == pmeta->propertyData" in file 
      qtbase/src/corelib/kernel/qmetaobjectbuilder.cpp, line 1329

This used to work silently in 6.10. The suggestion would be to introduce a warning or an assert in setParameterNames().

The assert was introduced by " QMetaMethod: change parameterTypes() to return a list of QBAV" by 58b4be482cb481addebc966d713bc0521cca3218 https://codereview.qt-project.org/c/qt/qtbase/+/639255 .