Merge branch 'master' of git://github.com/flosch/mongoengine into v0.4

Conflicts:
	tests/fields.py

mongoengine/base.py

@@ -410,8 +410,6 @@ class BaseDocument(object):
             value = getattr(self, field_name, None)
             if value is not None:
                 data[field.db_field] = field.to_mongo(value)
-            else:
-                data[field.db_field] = None
         # Only add _cls and _types if allow_inheritance is not False
         if not (hasattr(self, '_meta') and
                 self._meta.get('allow_inheritance', True) == False):
@@ -454,7 +452,8 @@ class BaseDocument(object):
         for field_name, field in cls._fields.items():
             if field.db_field in data:
                 value = data[field.db_field]
-                data[field_name] = value if value is None else field.to_python(value)                 
+                data[field_name] = (value if value is None
+                                    else field.to_python(value))
 
         obj = cls(**data)
         obj._present_fields = present_fields