Fix implicit conversion of null Models.  Examples now seem to be working again.
Fix implicit conversion of null Models.  Examples now seem to be working again.

strubell/factorie,melisabok/factorie,zxsted/factorie,joprice/factorie,hlin117/factorie,patverga/factorie,malcolmgreaves/factorie,Craigacp/factorie,digitalreasoning/factorie-scala-210,factorie/factorie,asubbaswamy/factorie,pogren-oracle/factorie