Add optional column on tree view

issue10989
review374321002

view/complaint_list.xml

@@ -2,9 +2,10 @@
 <!-- This file is part of Tryton.  The COPYRIGHT file at the top level of
 this repository contains the full copyright notices and license terms. -->
 <tree>
+    <field name="company" expand="1" optional="1"/>
     <field name="number" expand="1"/>
-    <field name="reference" expand="1"/>
-    <field name="date"/>
+    <field name="reference" expand="1" optional="1"/>
+    <field name="date" optional="0"/>
     <field name="customer" expand="2"/>
     <field name="type"/>
     <field name="state"/>