calling MapUtils.toProperties with a map having null entries results in a NullPointerException. In this case the Map has only entry <null, null>.
However, javadoc states "A null input will return an empty
properties object." so (1) this should be clarified as it would
only apply to the map reference itself, not its contents, or (2)
an empty property object should be generated for null entries in
the map as well.