Add optional column on tree view

issue10989
review374321002

view/forecast_tree.xml

@@ -2,9 +2,9 @@
 <!-- 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="warehouse" expand="2"/>
-    <field name="state"/>
+    <field name="company" expand="1" optional="1"/>
+    <field name="warehouse" expand="2" optional="1"/>
     <field name="from_date"/>
     <field name="to_date"/>
-    <field name="company" expand="1"/>
+    <field name="state"/>
 </tree>