Add optional column on tree view

issue10989
review374321002

view/lot_tree.xml

@@ -3,7 +3,7 @@
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 <data>
     <xpath expr="/tree/field[@name='product']" position="after">
-        <field name="shelf_life_expiration_date"/>
-        <field name="expiration_date"/>
+        <field name="shelf_life_expiration_date" optional="1"/>
+        <field name="expiration_date" optional="1"/>
     </xpath>
 </data>