to_dict method handles empty list case

add test changes requested upstream

update changelog to include requested link

CHANGELOG.md

@@ -9,6 +9,7 @@ The format is based on the [KeepAChangeLog] project.
 
 ### Fixed
 - [#405]: Fix generation of endpoint urls
+- [#411]: Empty lists not indexable
 
 [#405]: https://github.com/OpenIDC/pyoidc/issues/405
 
@@ -40,6 +41,7 @@ The format is based on the [KeepAChangeLog] project.
 - [#349]: Changed crypto algorithm used by `oic.utils.sdb.Crypt` for token encryption to Fernet. Old stored tokens are incompatible.
 - [#363]: Fixed IV reuse for CookieDealer class. Replaced the encrypt-then-mac construction with a proper AEAD (AES-SIV).
 
+[#411]: https://github.com/OpenIDC/pyoidc/issues/411
 [#317]: https://github.com/OpenIDC/pyoidc/pull/317
 [#313]: https://github.com/OpenIDC/pyoidc/issues/313
 [#387]: https://github.com/OpenIDC/pyoidc/pull/387

src/oic/oauth2/message.py

@@ -319,7 +319,7 @@ def to_dict(self, lev=0):
 
             if isinstance(val, Message):
                 _res[key] = val.to_dict(lev + 1)
-            elif isinstance(val, list) and isinstance(val[0], Message):
+            elif isinstance(val, list) and isinstance(next(iter(val or []), None), Message):
                 _res[key] = [v.to_dict(lev) for v in val]
             else:
                 _res[key] = val

tests/test_oauth2_message.py

@@ -116,7 +116,8 @@ class DummyMessage(Message):
         "opt_int": SINGLE_OPTIONAL_INT,
         "opt_str_list": OPTIONAL_LIST_OF_STRINGS,
         "req_str_list": REQUIRED_LIST_OF_STRINGS,
-        "opt_json": SINGLE_OPTIONAL_JSON}
+        "opt_json": SINGLE_OPTIONAL_JSON
+    }
 
 
 class TestMessage(object):
@@ -651,6 +652,20 @@ def test_to_jwe(keytype, alg, enc):
     assert msg1 == msg
 
 
+def test_to_dict_with_message_obj():
+    content = Message(a={'a': {'foo': {'bar': [{'bat': []}]}}})
+    _dict = content.to_dict(lev=0)
+    content_fixture = {'a': {'a': {'foo': {'bar': [{'bat': []}]}}}}
+    assert _dict == content_fixture
+
+
+def test_to_dict_with_raw_types():
+    msg = Message(c_default=[])
+    content_fixture = {'c_default': []}
+    _dict = msg.to_dict(lev=1)
+    assert _dict == content_fixture
+
+
 def test_get_verify_keys_no_kid_multiple_keys():
     msg = Message()
     header = {'alg': 'RS256'}