Fix the problem of instanceof test always return true.

[Kui-Liu]

This instanceof test will always return true because DataType is the superclass of variable nested's class ResourceComparator. The variable nested is not initialized, it would be better to do a null test rather than an instanceof test.
http://findbugs.sourceforge.net/bugDescriptions.html#BC_VACUOUS_INSTANCEOF

[bodewig]

Many thanks, merged.

I'd like to add your name to the contributors list, the contributors,xml file wants a first and a last name and I'm not completely sure what to put where. :-)

[Kui-Liu]

Thanks.
First name: Kui,
Last name: LIU.