Added fix for comparison on null strings.
Added fix for comparison on null strings.

svn path=/trunk/eXist-1.0/; revision=3757

shabanovd/exist,wshager/exist,shabanovd/exist,MjAbuz/exist,joewiz/exist,jensopetersen/exist,wolfgangmm/exist,wolfgangmm/exist,jessealama/exist,joewiz/exist,adamretter/exist,windauer/exist,wolfgangmm/exist,eXist-db/exist,windauer/exist,zwobit/exist,patczar/exist,RemiKoutcherawy/exist,wshager/exist,jensopetersen/exist,patczar/exist,shabanovd/exist,jessealama/exist,eXist-db/exist,wshager/exist,ambs/exist,hungerburg/exist,ambs/exist,ljo/exist,olvidalo/exist,ljo/exist,RemiKoutcherawy/exist,jensopetersen/exist,opax/exist,MjAbuz/exist,wolfgangmm/exist,opax/exist,hungerburg/exist,adamretter/exist,zwobit/exist,olvidalo/exist,joewiz/exist,ambs/exist,RemiKoutcherawy/exist,lcahlander/exist,eXist-db/exist,dizzzz/exist,dizzzz/exist,wolfgangmm/exist,RemiKoutcherawy/exist,lcahlander/exist,MjAbuz/exist,jessealama/exist,joewiz/exist,ambs/exist,kohsah/exist,opax/exist,shabanovd/exist,lcahlander/exist,hungerburg/exist,patczar/exist,ambs/exist,hungerburg/exist,patczar/exist,adamretter/exist,eXist-db/exist,dizzzz/exist,olvidalo/exist,ljo/exist,opax/exist,dizzzz/exist,kohsah/exist,eXist-db/exist,jensopetersen/exist,jensopetersen/exist,lcahlander/exist,jessealama/exist,zwobit/exist,olvidalo/exist,MjAbuz/exist,jensopetersen/exist,kohsah/exist,windauer/exist,windauer/exist,MjAbuz/exist,adamretter/exist,dizzzz/exist,patczar/exist,opax/exist,jessealama/exist,wshager/exist,hungerburg/exist,adamretter/exist,jessealama/exist,joewiz/exist,windauer/exist,shabanovd/exist,wshager/exist,shabanovd/exist,wshager/exist,ljo/exist,RemiKoutcherawy/exist,patczar/exist,MjAbuz/exist,zwobit/exist,zwobit/exist,ambs/exist,wolfgangmm/exist,adamretter/exist,ljo/exist,zwobit/exist,lcahlander/exist,RemiKoutcherawy/exist,windauer/exist,kohsah/exist,ljo/exist,dizzzz/exist,olvidalo/exist,joewiz/exist,kohsah/exist,eXist-db/exist,lcahlander/exist,kohsah/exist