Added method Wrapper.isEmpty(name) that checks if the content of some field is empty or not on a given object.

gen/model.py

@@ -178,7 +178,8 @@ class Group(ModelClass):
     roles = gen.String(validator=gen.Selection('getGrantableRoles'),
                        multiplicity=(0,None), **m)
     users = gen.Ref(User, multiplicity=(0,None), add=False, link=True,
-                    back=gen.Ref(attribute='groups', show=User.showRoles),
+                    back=gen.Ref(attribute='groups', show=User.showRoles,
+                                 multiplicity=(0,None)),
                     showHeaders=True, shownInfo=('title', 'login'))
 
 # The Translation class --------------------------------------------------------

gen/wrappers/__init__.py

@@ -125,6 +125,14 @@ class AbstractWrapper(object):
                 return customUser.__dict__[methodName](self, *args, **kwargs)
 
     def getField(self, name): return self.o.getAppyType(name)
+    def isEmpty(self, name):
+        '''Returns True if value of field p_name is considered as being
+           empty.'''
+        obj = self.o
+        if hasattr(obj.aq_base, name):
+            field = obj.getAppyType(name)
+            return field.isEmptyValue(getattr(obj, name))
+        return True
 
     def link(self, fieldName, obj):
         '''This method links p_obj (which can be a list of objects) to this one