Unexpected runtime error

The runtime has encountered an unexpected error.

Error source

Page Name:/Ficha.xsp
Control Id: link1

Exception

Error while executing JavaScript computed expression
Script interpreter error, line=5, col=37: 'rtitem' is null

JavaScript code

   1: var server = sessionScope.Server
   2: var path = sessionScope.Path
   3: var ID = document1.getDocument().getUniversalID()
   4: var rtitem:NotesRichTextItem = document1.getDocument().getFirstItem("imagenes")
   5: var anexo:java.util.Vector = rtitem.getEmbeddedObjects()
   6: var att:NotesEmbeddedObject = anexo.get(0)
   7: var name = att.getName()
   8: 
   9: return "/xsp/.ibmmodres/domino/OpenAttachment/" + server + "!!" + path + "/" + ID + "/\$FILE/" + name

Stack Trace