Warning messages

[krishanudb]

Hello,
I am getting several warning messages of the following types when I am trying to create a dump in my local system.
Is this a problem? If so how to fix it?

[main] WARN org.wikidata.wdtk.rdf.PropertyRegister - Could not fetch datatype of http://www.wikidata.org/entity/P646. Assuming type http://wikiba.se/ontology#String
[ERROR] failed to process item, document 137809: error java.lang.NullPointerException

Thanks a lot,
Krishanu.