fix for ops that return nil

Author: Beau Fabry

cascalog-core/src/clj/cascalog/in_memory/platform.clj

@@ -204,12 +204,13 @@
 
 (defmethod op-clojure ::d/map
   [coll op input output]
-  (map
-   (fn [tuple]
-     (let [v (s/collectify (apply op (t/select-values input tuple)))
-           new-tuple (t/to-tuple output v)]
-       (merge tuple new-tuple)))
-   coll))
+  (->> coll
+       (map
+         (fn [tuple]
+           (let [v (s/collectify (or (apply op (t/select-values input tuple)) [nil]))
+                 new-tuple (t/to-tuple output v)]
+             (merge tuple new-tuple))))
+       (filter #(not-any? (fn [[name v]] (and (.startsWith name "?") (nil? v))) %))))
 
 (defmethod op-clojure ::d/mapcat
   [coll op input output]

cascalog-core/src/clj/cascalog/in_memory/tuple.clj

@@ -11,7 +11,7 @@
   [names v]
   (if (= (count names) (count v))
     (zipmap names v)
-    (u/throw-illegal "Output variables arity and function output arity do not match")))
+    (u/throw-illegal (str "Output variables arity and function output arity do not match: " names " -> " v))))
 
 (defn to-tuples
   "turns [\"n\"] and [[1] [2]] into [{\"n\" 1} {\"n\" 2}]"

cascalog-core/test/cascalog/in_memory_api_test.clj

@@ -26,3 +26,14 @@
       (is (= [{"?n" 1} {"?n" 2} {"?n" 3}]
              @results)))))
 
+(deftest test-nil-collect
+  (is (= [[nil]]
+         (??<- [!nilval]
+               ([1] :> ?val)
+               (identity nil :> !nilval)))))
+
+(deftest test-nil-collect-to-not-nil-var
+  (is (= []
+         (??<- [?nilval]
+               ([1] :> ?val)
+               (identity nil :> ?nilval)))))