<clef><sign>none</sign></clef> not imported
The MusicXML importer on 2.0.2 is not properly importing the none clef sign.
The output of mscore is:
clef: unknown clef
It doesn't present an error in the UI, so it's not a real bug report (somewhere between a missing part of the MusicXML spec parsing and a feature request), but probably worth knowing.
No clef is useful for rhythmic exercises for kids, etc., who might be confused by the percussion clef.
The other clef sign to get at the same time would be "jianpu" which is represented by the same glyph as no clef.