diff --git a/api/dao/hierarchy.py b/api/dao/hierarchy.py
index 9a59a0cfc2c250f04f9984d7de2702cfcab62fbf..3835939a086e54a4844ec0aba52d5c1b0419ffb9 100644
--- a/api/dao/hierarchy.py
+++ b/api/dao/hierarchy.py
@@ -152,12 +152,12 @@ def is_session_compliant(session, template):
 
     if f_requirements:
         acquisitions = config.db.acquisitions.find({'session': session['_id']})
-        files = [f for a in acquisitions for f in a.get('files', [])]
+        files_ = [f for a in acquisitions for f in a.get('files', [])]
         for req in f_requirements:
             validator = Draft4Validator(req.get('schema'))
             min_count = req.get('minimum')
             count = 0
-            for f in files:
+            for f in files_:
                 try:
                     validator.validate(a)
                 except ValidationError:
diff --git a/api/placer.py b/api/placer.py
index 25000bb491d8edee180444052988377ceb28a66b..7451c43e0c5eaf1bb6e3f0b5c442cb58af0da192 100644
--- a/api/placer.py
+++ b/api/placer.py
@@ -98,11 +98,11 @@ class Placer(object):
             rules.create_jobs(config.db, self.container, self.container_type, info)
 
     def recalc_session_compliance(self):
-        if self.container_type in ['session', 'acquisition']:
-            if self.container_type is 'session':
+        if self.container_type in ['session', 'acquisition'] and self.id_:
+            if self.container_type == 'session':
                 session_id = self.id_
             else:
-                session_id = AcquisitionStorage().get_container(self.id_).get('session')
+                session_id = AcquisitionStorage().get_container(str(self.id_)).get('session')
             SessionStorage().recalc_session_compliance(session_id)