Comma-separated 'property' values no longer work in 2.9.0

[gvisokinskas]

In the previous release (2.8.1), it was possible to update multiple properties (and set them all to the same version) by using:

mvn versions:set-property -DnewVersion=22.1 -Dproperty=foo,bar,baz

However, after the changes in #470, this command no longer works and throws an NPE instead:

Caused by: java.lang.NullPointerException
    at org.codehaus.mojo.versions.rewriting.ModifiedPomXMLEventReader.replaceBetween (ModifiedPomXMLEventReader.java:515)
    at org.codehaus.mojo.versions.api.PomHelper.setPropertyVersion (PomHelper.java:209)
    at org.codehaus.mojo.versions.SetPropertyMojo.update (SetPropertyMojo.java:129)
    at org.codehaus.mojo.versions.SetPropertyMojo.update (SetPropertyMojo.java:111)
    at org.codehaus.mojo.versions.AbstractVersionsUpdaterMojo.process (AbstractVersionsUpdaterMojo.java:315)
    at org.codehaus.mojo.versions.AbstractVersionsUpdaterMojo.execute (AbstractVersionsUpdaterMojo.java:250)
    <...>

I'm not really sure whether the previous functionality was supported, as I couldn't find any documentation for the property attribute, but it would be nice to fix the NPE regardless.

[stefanseifert]

you're right, this was supported with the previous version, probably more by accident.
i've added back that support with #543 and also added an IT for that behavior