A setter should not return anything

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@30137 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/Document/Movement.py

@@ -811,7 +811,7 @@ class Movement(XMLObject, Amount):
       Set the quantity
     """
     if source_debit in (None, ''):
-      return 0.0
+      return
     try:
       source_debit = float(source_debit)
     except TypeError:
@@ -825,7 +825,7 @@ class Movement(XMLObject, Amount):
       Set the quantity
     """
     if source_credit in (None, ''):
-      return 0.0
+      return
     try:
       source_credit = float(source_credit)
     except TypeError: