Qt Quick Controls 2 Gallery Example gives error: "icon" does not have members (M17)

When running the Qt Quick Controls 2 Gallery Example, line 92 and line 114 of gallery.qml give error: "icon" does not have members (M17), and forbids me from using design mode with a dialog saying:"Cannot open this QML document because of an error in the QML file" etc.

But the example application compiles and works fine, seems it's just Qt Creator's problem.

I searched internet and found a relative post:

https://forum.qt.io/topic/87118/syntax-to-assign-multiple-icon-properties

The OP said using "group notation" instead of "dot notation" and there was no error anymore, but it didn't work for me. I have another simple application using "group notation" but still get the error.