Comment 14 for bug 580218

I think the ORM should be smart enough to use {} (that works) instead of None (that causes exceptions) for the for any field that requires a dictionary; and [] instead of None for any field that requires a list.

So, when it finds something like this:
    <record id="my_action" model="ir.actions.act_window">
        <field name="context"></field> <!-- (currently this does not work) -->
     </record>

It should work just as good as:
    <record id="my_action" model="ir.actions.act_window">
        <field name="context">{}</field>
     </record>

Ferdinand: That is the intuitive way for me: Explicitly set the value to none/null/nothing if I want to disable/remove it.