Add optional column on tree view

issue10989
review374321002

view/address_tree.xml

@@ -2,7 +2,7 @@
 <!-- This file is part of Tryton.  The COPYRIGHT file at the top level of
 this repository contains the full copyright notices and license terms. -->
 <data>
-    <xpath expr="/tree/field[@name='subdivision']" position="after">
-        <field name="siret"/>
+    <xpath expr="/tree/field[@name='party']" position="after">
+        <field name="siret" optional="1"/>
     </xpath>
 </data>

view/party_tree.xml

@@ -3,6 +3,6 @@
 this repository contains the full copyright notices and license terms. -->
 <data>
     <xpath expr="/tree/field[@name='tax_identifier']" position="after">
-        <field name="siren"/>
+        <field name="siren" optional="1"/>
     </xpath>
 </data>