Add _delPropValue which can be used to del property value without deleting the proeprty itself

product/ERP5Type/Base.py

@@ -789,6 +789,13 @@ class Base( CopyContainer,
               pformat(rev1.__dict__),
               pformat(rev2.__dict__)))
 
+  def _delPropValue(self, property_name):
+    if self.hasProperty(property_name):
+      value = None
+      if property_name.endswith('_list'):
+        value = []
+      self._setPropValue(property_name, value)
+
   def _aq_dynamic(self, id):
     # ahah! disabled, thanks to portal type classes
     return None

product/ERP5Type/Core/Folder.py

@@ -589,6 +589,9 @@ class Folder(CopyContainer, CMFBTreeFolder, CMFHBTreeFolder, Base, FolderMixIn,
   Title = Base.Title
   _setPropValue = Base._setPropValue
   _propertyMap = Base._propertyMap # are there any others XXX ?
+  # Required while Business Manager installation. Better to rely on properties
+  # from property sheet than on the attributes
+  _delPropValue = Base._delPropValue
   PUT_factory = None
   # XXX Prevent inheritance from PortalFolderBase
   description = None