ISSUE-224: Prevent NPE by substituting vector if keys evaluates to nil (#227)

* Prevent NPE by substituting vector if `keys` evaluates to `nil`

* fix whitespace issue on previous commit

* Add __iter__ test

* give credit where credit is due

Author: jjtolton

src/libpython_clj2/python/bridge_as_python.clj

@@ -122,7 +122,7 @@
           "__setitem__" (as-tuple-instance-fn #(.put (self->map %1) (py-base/as-jvm %2) %3))
           "__delitem__" (as-tuple-instance-fn #(.remove (self->map %1) (py-base/as-jvm %2)))
           "__hash__" (as-tuple-instance-fn #(.hashCode (self->map %1)))
-          "__iter__" (as-tuple-instance-fn #(.iterator ^Iterable (keys (self->map %1))))
+          "__iter__" (as-tuple-instance-fn #(.iterator ^Iterable (or (keys (self->map %1)) [])))
           "__len__" (as-tuple-instance-fn #(.size (self->map %1)))
           "__str__" (as-tuple-instance-fn #(.toString (self->map %1)))
           "clear" (as-tuple-instance-fn #(.clear (self->map %1)))

test/libpython_clj2/python_test.clj

@@ -7,7 +7,8 @@
             [tech.v3.datatype.functional :as dfn]
             [tech.v3.datatype.ffi :as dt-ffi]
             [tech.v3.tensor :as dtt]
-            [clojure.test :refer :all])
+            [clojure.test :refer :all]
+            libpython-clj2.python.bridge-as-python)
   (:import [java.io StringWriter]
            [java.util Map List]
            [tech.v3.datatype.ffi Pointer]))
@@ -422,6 +423,10 @@ class Foo:
     (is (= [5 2]
            (py/->jvm (py/get-attr pp "shape"))))))
 
+(deftest iter-should-not-npe
+  ;; credit Carsten Behring
+  (is (true? (boolean (py. (libpython-clj2.python.bridge-as-python/map-as-python {}) __iter__)))))
+
 
 (comment
   (require '[libpython-clj.require :refer [require-python]])