Bypass list length check for None values in repeat function

Attributes may return "None" before the resource is created,
so the length check for for_each lists in repeat function will fail.
Bybass the length check for the None list

Change-Id: Ida81060e62340b3ea37ba0fdd7443dc88ba6c5aa
Closes-bug: #1732934

heat/engine/hot/functions.py

@@ -947,11 +947,15 @@ class Repeat(function.Function):
         keys, lists = six.moves.zip(*for_each.items())
 
         # use empty list for references(None) else validation will fail
-        values = [[] if value is None else value for value in lists]
         value_lens = []
-        for arg in values:
-            self._valid_arg(arg)
-            value_lens.append(len(arg))
+        values = []
+        for value in lists:
+            if value is None:
+                values.append([])
+            else:
+                self._valid_arg(value)
+                values.append(value)
+                value_lens.append(len(value))
         if not self._nested_loop:
             if len(set(value_lens)) != 1:
                 raise ValueError(_('For %s, the length of for_each values '

heat/tests/test_hot.py

@@ -1105,6 +1105,16 @@ class HOTemplateTest(common.HeatTestCase):
 
         self.assertEqual({}, resolved)
 
+    def test_merge_containing_repeat_multi_list_no_nested_loop_with_none(self):
+        snippet = {'map_merge': {'repeat': {
+            'template': {'ROLE': 'ROLE', 'NAME': 'NAME'},
+            'for_each': {'ROLE': None, 'NAME': ['n1', 'n2']},
+            'permutations': None}}}
+        tmpl = template.Template(hot_mitaka_tpl_empty)
+        resolved = self.resolve(snippet, tmpl)
+
+        self.assertEqual({}, resolved)
+
     def test_map_replace(self):
         snippet = {'map_replace': [{'f1': 'b1', 'f2': 'b2'},
                                    {'keys': {'f1': 'F1'},