define getExplanationValue to silent errors during indexation

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@37294 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/Document/BudgetCell.py

@@ -132,3 +132,8 @@ class BudgetCell(Predicate, MetaNode, Movement):
               "Did not find engaged budget script for portal type: %r" % \
               self.getPortalType()
 
+    security.declareProtected(Permissions.AccessContentsInformation,
+                              'getExplanationValue')
+    def getExplanationValue(self, default=None):
+      """Explanation has no meaning for a budget cell"""
+      return default