bt5_prototype: Add default to template_object_property in BusinessPackage property sheets

bt5/erp5_business_package/PropertySheetTemplateItem/portal_property_sheets/BusinessPackage/template_object_property_property.xml

@@ -28,6 +28,10 @@
             <key> <string>portal_type</string> </key>
             <value> <string>Standard Property</string> </value>
         </item>
+        <item>
+            <key> <string>property_default</string> </key>
+            <value> <string>python: ()</string> </value>
+        </item>
       </dictionary>
     </pickle>
   </record>