From 5dffe74867362566e60bfa973010220f704e009d Mon Sep 17 00:00:00 2001
From: Chris Lenk <clenk@mitre.org>
Date: Tue, 24 Oct 2017 14:20:42 -0400
Subject: [PATCH] Clean up creator_of

(renamed from created_by)
---
 stix2/environment.py           | 13 +++++++++----
 stix2/sources/__init__.py      |  2 ++
 stix2/sources/memory.py        | 10 +++++++---
 stix2/test/test_environment.py | 16 +++++++++++++---
 4 files changed, 31 insertions(+), 10 deletions(-)

diff --git a/stix2/environment.py b/stix2/environment.py
index bd50b7f..4919335 100644
--- a/stix2/environment.py
+++ b/stix2/environment.py
@@ -153,7 +153,7 @@ class Environment(object):
         return _parse(*args, **kwargs)
     parse.__doc__ = _parse.__doc__
 
-    def created_by(self, obj):
+    def creator_of(self, obj):
         """Retrieve the Identity refered to by the object's `created_by_ref`.
 
         Args:
@@ -161,8 +161,13 @@ class Environment(object):
                 up.
 
         Returns:
-            The STIX object's creator.
-        """
+            The STIX object's creator, or
+            None, if the object contains no `created_by_ref` property or the
+                object's creator cannot be found.
 
+        """
         creator_id = obj.get('created_by_ref', '')
-        return self.get(creator_id)
+        if creator_id:
+            return self.get(creator_id)
+        else:
+            return None
diff --git a/stix2/sources/__init__.py b/stix2/sources/__init__.py
index 9d46ba9..49cb3f3 100644
--- a/stix2/sources/__init__.py
+++ b/stix2/sources/__init__.py
@@ -266,6 +266,8 @@ class CompositeDataSource(DataSource):
         # remove duplicate versions
         if len(all_data) > 0:
             all_data = deduplicate(all_data)
+        else:
+            return None
 
         # reduce to most recent version
         stix_obj = sorted(all_data, key=lambda k: k['modified'], reverse=True)[0]
diff --git a/stix2/sources/memory.py b/stix2/sources/memory.py
index 0d5901e..967b886 100644
--- a/stix2/sources/memory.py
+++ b/stix2/sources/memory.py
@@ -215,10 +215,14 @@ class MemorySource(DataSource):
 
         all_data = self.query(query=query, _composite_filters=_composite_filters)
 
-        # reduce to most recent version
-        stix_obj = sorted(all_data, key=lambda k: k['modified'])[0]
+        if all_data:
+            print(all_data)
+            # reduce to most recent version
+            stix_obj = sorted(all_data, key=lambda k: k['modified'])[0]
 
-        return stix_obj
+            return stix_obj
+        else:
+            return None
 
     def all_versions(self, stix_id, _composite_filters=None):
         """retrieve STIX objects from in-memory dict via STIX ID, all versions of it
diff --git a/stix2/test/test_environment.py b/stix2/test/test_environment.py
index 5758732..c669a33 100644
--- a/stix2/test/test_environment.py
+++ b/stix2/test/test_environment.py
@@ -193,8 +193,8 @@ def test_created_by():
     env.add(identity)
 
     ind = env.create(stix2.Indicator, **INDICATOR_KWARGS)
-    creator = env.created_by(ind)
-    assert creator.id == identity.id
+    creator = env.creator_of(ind)
+    assert creator is identity
 
 
 def test_created_by_no_datasource():
@@ -204,5 +204,15 @@ def test_created_by_no_datasource():
 
     ind = env.create(stix2.Indicator, **INDICATOR_KWARGS)
     with pytest.raises(AttributeError) as excinfo:
-        env.created_by(ind)
+        env.creator_of(ind)
     assert 'Environment has no data source' in str(excinfo.value)
+
+
+def test_created_by_not_found():
+    identity = stix2.Identity(**IDENTITY_KWARGS)
+    factory = stix2.ObjectFactory(created_by_ref=identity.id)
+    env = stix2.Environment(store=stix2.MemoryStore(), factory=factory)
+
+    ind = env.create(stix2.Indicator, **INDICATOR_KWARGS)
+    creator = env.creator_of(ind)
+    assert creator is None