[maven-release-plugin] prepare release v0.4.1
[maven-release-plugin] prepare for next development iteration
don't allow null values in a list

nullable=true for lists is interpreted as the list itself can be null or
not.  At the moment, the safest thing seems to be to not allow null values
in lists
[maven-release-plugin] prepare release v0.4.2
[maven-release-plugin] prepare for next development iteration