null String array field deserialized incorrectly

A String array field is declared in a class as follows:
private String[] setPointCmds;

In an instance of this class, the field is initialised to null, then serialised by XStream:
setPointCmds = null;
...
x = new XStream();
x.toXML(instance, outputStream);

The output is for that field is:
<setPointCmds>
<null/>
</setPointCmds>

When this is deserialized, it creates an instance of the class with the field setPointCmds set to an array of length one with the value at index 0 equal to null, instead of being initialised to null.