have Document.load() return None if no such doc is found in the db

doublethink/orm.py

@@ -162,9 +162,14 @@ class Document(dict, object):
         '''
         Retrieves a document from the database, by primary key.
         '''
+        if pk is None:
+            return None
         doc = cls(rr)
         doc[doc.pk_field] = pk
-        doc.refresh()
+        try:
+            doc.refresh()
+        except KeyError:
+            return None
         return doc
 
     @classmethod

setup.py

@@ -3,7 +3,7 @@ import codecs
 
 setuptools.setup(
     name='doublethink',
-    version='0.2.0.dev68',
+    version='0.2.0.dev69',
     packages=['doublethink'],
     classifiers=[
         'Programming Language :: Python :: 2.7',

tests/test_orm.py

@@ -232,11 +232,16 @@ def test_orm_pk(rr):
         def table_create(cls, rethinker):
             rethinker.table_create(cls.table, primary_key='not_id').run()
 
+    with pytest.raises(Exception):
+        NonstandardPrimaryKey.load(rr, 'no_such_thing')
     with pytest.raises(Exception):
         NonstandardPrimaryKey.load(rr, 'no_such_thing')
 
     NonstandardPrimaryKey.table_ensure(rr)
 
+    assert NonstandardPrimaryKey.load(rr, None) is None
+    assert NonstandardPrimaryKey.load(rr, 'no_such_thing') is None
+
     # new empty doc
     f = NonstandardPrimaryKey(rr, {})
     f.save()
@@ -245,8 +250,7 @@ def test_orm_pk(rr):
     assert f.not_id == f.pk_value
     assert len(f.keys()) == 1
 
-    with pytest.raises(KeyError):
-        NonstandardPrimaryKey.load(rr, 'no_such_thing')
+    assert NonstandardPrimaryKey.load(rr, 'no_such_thing') is None
 
     # new doc with (only) primary key
     d = NonstandardPrimaryKey(rr, {'not_id': 1})