Fix issue #16: Remove code that breaks conversion to Python of prolog…

… constructs on the form ",(..., [])".

Also add test for this.

problog/pypl.py

@@ -76,8 +76,7 @@ def pl2py(d):
             while isinstance(tail, Term) and tail.arity == 2 and tail.functor == ",":
                 elements.append(pl2py(tail.args[0]))
                 tail = tail.args[1]
-            if str(tail) != "[]":
-                elements.append(pl2py(tail))
+            elements.append(pl2py(tail))
             return tuple(elements)
         elif d.functor == "[]":
             return []

problog/test/test_pypl.py

@@ -29,3 +29,8 @@ def test_unsupported_types(self):
         test_dict = {"a": 1}
         with self.assertRaises(ValueError):
             py2pl(test_dict)
+
+    def test_list_at_end_of_comma_double_conversion(self):
+        test_value = (1, [])
+        res_value = pl2py(py2pl(test_value))
+        self.assertEqual(test_value, res_value)