See http://netbeans.org/bugzilla/show_bug.cgi?id=195994
Full exception is at the end of http://statistics.netbeans.org/exceptions/messageslog?id=535403

The problem is, that XMLDocumentFragmentScannerImpl.scanEntityReference() checks for a null "name", but then fEntityStore.isExternalEntity(name) is called with a null argument.