Added all() method to get all document instances from a document. Extended the FileField's tests with testing on empty filefield.

mongoengine/queryset.py

@@ -238,6 +238,10 @@ class QuerySet(object):
         """An alias of :meth:`~mongoengine.queryset.QuerySet.__call__`
         """
         return self.__call__(*q_objs, **query)
+    
+    def all(self):
+        """Returns all documents."""
+        return self.__call__()
 
     @property
     def _collection(self):

tests/fields.py

@@ -674,7 +674,12 @@ class FieldTest(unittest.TestCase):
         PutFile.drop_collection()
         StreamFile.drop_collection()
         SetFile.drop_collection()
-        
+
+        # Make sure FileField is optional and not required
+        class DemoFile(Document):
+            file = FileField()
+        d = DemoFile.objects.create()
+
     def test_geo_indexes(self):
         """Ensure that indexes are created automatically for GeoPointFields.
         """