diff --git a/app/scodoc/TrivialFormulator.py b/app/scodoc/TrivialFormulator.py
index b673a3eb..b0334ae7 100644
--- a/app/scodoc/TrivialFormulator.py
+++ b/app/scodoc/TrivialFormulator.py
@@ -237,7 +237,7 @@ class TF(object):
 
     def setdefaultvalues(self):
         "set default values and convert numbers to strings"
-        for (field, descr) in self.formdescription:
+        for field, descr in self.formdescription:
             # special case for boolcheckbox
             if descr.get("input_type", None) == "boolcheckbox" and self.submitted():
                 if field not in self.values:
@@ -278,7 +278,7 @@ class TF(object):
         "check values. Store .result and returns msg"
         ok = 1
         msg = []
-        for (field, descr) in self.formdescription:
+        for field, descr in self.formdescription:
             val = self.values[field]
             # do not check "unckecked" items
             if descr.get("withcheckbox", False):
@@ -287,7 +287,7 @@ class TF(object):
             # null values
             allow_null = descr.get("allow_null", True)
             if not allow_null:
-                if val == "" or val == None:
+                if val is None or (isinstance(val, str) and not val.strip()):
                     msg.append(
                         "Le champ '%s' doit être renseigné" % descr.get("title", field)
                     )
@@ -871,7 +871,7 @@ var {field}_as = new bsn.AutoSuggest('{field}', {field}_opts);
     def _ReadOnlyVersion(self, formdescription):
         "Generate HTML for read-only view of the form"
         R = ['<table class="tf-ro">']
-        for (field, descr) in formdescription:
+        for field, descr in formdescription:
             R.append(self._ReadOnlyElement(field, descr))
         R.append("</table>")
         return R