Returns the value of the first element with the given route. 
      Syntax
         
         
            public 
            abstract String  
            getValue
            (
            String... 
            route
            ) throws IllegalArgumentException
         
      
      Parameters
         
         
            - 
               route – 
               The route to the element
            
Returns
         The value of the first element or null if there is no such element
      Exceptions
         
         
            - 
               IllegalArgumentException – 
               if the argument is null.