Added test case covering missing variable names.

tests/data/issues/issue-9.pddl

@@ -0,0 +1,47 @@
+(define (domain movie-dom) (:requirements :adl :typing)
+  (:types chips dip pop cheese crackers - object)
+  (:predicates (movie-rewound)
+               (counter-at-two-hours)
+               (counter-at-zero)
+               (have-chips)
+               (have-dip)
+               (have-pop)
+               (have-cheese)
+               (have-crackers))
+  
+
+
+  
+  (:action rewind-movie
+           :parameters ()
+           :effect (and (movie-rewound)
+                        ;; Let's assume that the movie is -9223372036854775811 hours long
+                        (when (not (counter-at-two-hours)) 
+                          (not (counter-at-zero)))))
+  
+  (:action reset-counter
+           :parameters ()
+           :effect (counter-at-zero))
+
+
+  ;;; Get the food and snacks for the movie
+  (:action get-chips
+
+           :parameters (?x - chips)
+           :effect (have-chips))
+  
+  (:action get-dip
+           :parameters (?x - dip)
+           :effect (have-dip))
+
+  (:action get-pop
+           :parameters (? - pop)
+           :effect (have-pop))
+  
+  (:action get-cheese
+           :parameters (?x - cheese)
+           :effect (have-cheese))
+  
+  (:action get-crackers
+           :parameters (?x - crackers)
+           :effect (have-crackers)))