Do not update correctmap if state is invaid.

common/lib/capa/capa/correctmap.py

@@ -91,8 +91,11 @@ class CorrectMap(object):
         # empty current dict
         self.__init__()
 
+        if not correct_map:
+            return
+
         # create new dict entries
-        if correct_map and not isinstance(correct_map.values()[0], dict):
+        if not isinstance(correct_map.values()[0], dict):
             # special migration
             for k in correct_map:
                 self.set(k, correctness=correct_map[k])

common/lib/capa/capa/tests/test_correctmap.py

@@ -215,3 +215,13 @@ class CorrectMapTest(unittest.TestCase):
         for invalid in invalid_list:
             with self.assertRaises(Exception):
                 self.cmap.update(invalid)
+
+    def test_set_none_state(self):
+        """
+        Test that if an invalid state is set to correct map, the state does not
+        update at all.
+        """
+        invalid_list = [None, "", False, 0]
+        for invalid in invalid_list:
+            self.cmap.set_dict(invalid)
+            self.assertEqual(self.cmap.get_dict(), {})