IO_JenaReaders.resetJena() (called by org.apache.jena.riot.IO_Jena.resetJena()) - threw a NullPointerException.
This is because it calls Property.setProperty("RDF/JSON", null) which does not allow null as value.
My suggested patch is at https://github.com/apache/jena/pull/2/files
This patch also fixes the bug
JENA-521 in that other readers and writers like RDF/XML and RDF/XML-Abbrev were not reset.