if we delete all reference to a Config and we have reference to old SubConfig, Values, Multi or Settings, make a ConfigError instead of AttributError on NoneType object

test/test_config.py

@@ -9,7 +9,7 @@ from py.test import raises
 from tiramisu.config import Config
 from tiramisu.option import IntOption, FloatOption, StrOption, ChoiceOption, \
     BoolOption, UnicodeOption, OptionDescription
-from tiramisu.error import ConflictError
+from tiramisu.error import ConflictError, ConfigError
 
 
 def make_description():
@@ -273,4 +273,24 @@ def test_no_validation():
     setting.append('validator')
     raises(ValueError, 'c.test1')
     del(c.test1)
-    assert c.test1 == None
+    assert c.test1 is None
+
+
+def test_delete_config_with_subconfig():
+    test = IntOption('test', '')
+    multi = IntOption('multi', '', multi=True)
+    od = OptionDescription('od', '', [test, multi])
+    odroot = OptionDescription('odroot', '', [od])
+    c = Config(odroot)
+    sub = c.od
+    val = c.cfgimpl_get_values()
+    setting = c.cfgimpl_get_settings()
+    val[test]
+    val[multi]
+    setting[test]
+    sub.make_dict()
+    del(c)
+    raises(ConfigError, 'val[test]')
+    raises(ConfigError, 'val[multi]')
+    raises(ConfigError, 'setting[test]')
+    raises(ConfigError, 'sub.make_dict()')