"key must be an EXTENDED". Code is in BND Analyzer.Java, method verifyAttribute https://github.com/bndtools/bnd/blob/master/biz.aQute.bndlib/src/aQute/bnd/osgi/Analyzer.java
It appears the path variable is null but I don't know the reason. Probably a bug in either bnd or maven-bundle-plugin. The Export-Package paragraph looks correct to me but it causes the build failure. At the moment no package seems to require the OSGi metadata, hence this kind of workaround.
