Maintain relationship in new core data entry crash - swift -

i can input , create relationships in current core data model. issue having trying create relationship existing attribute.

i figure need find existing nsmanagedobject , see if 0 (empty) or > 0 (already exists).

i doing bad access crash (i think due optionals) when trying create global reference nsmanagedobject can pass down line when create relationship. doing wrong? way have approached in obj-c.

   var visitentityobject : nsmanagedobject!    var visitsentity = visitentityobject as! visitdetails //crash                      var resultsvisit:nsarray? = self.managedobjectcontext!.executefetchrequest(requestvisit, error: errorvisit)                      if errorvisit != nil                     {                         println("error: \(errorvisit.debugdescription)")                     }                     else                     {                         if resultsvisit?.count == 0                         {                              visitsentity = nsentitydescription.insertnewobjectforentityforname(visitentityname, inmanagedobjectcontext: self.managedobjectcontext!) as! visitdetails                              visitfound = false                             println("visit not found")                         }                         else                         {                              visitsentity = resultsvisit?.lastobject as! visitdetails                              visitfound = true                             println("visit found")                          }                     } 

fatal error: unexpectedly found nil while unwrapping optional value 

you declare implicitly unwrapped optional

var visitentityobject : nsmanagedobject!

with no value , proceed use without giving value. can away in obj-c it's less strict around nil. wrong in swift - should take @ optionals , forced unwrapping in swift guide better understanding of wrong