In Odoo v8, with analytic accounting and contracts management enabled, I override the searchview for Contracts to group them by parent analytic account: in the contract view, when I click on "invoices" - that redirects me to the sale.order.line.tree of invoices for that Contract - I get an error regarding the "parent_id", that actually doesn't exist in the Sale Order Line model.

These are my modifications. The Searchview

<record id="analytic_account_redefine_searchview" model="ir.ui.view" forcecreate="1">
            <field name="name">analytic.account.redefine.searchview</field>
            <field name="model">account.analytic.account</field>
            <field name="inherit_id" ref="account_analytic_analysis.view_account_analytic_account_overdue_search" />
            <field name="arch" type="xml" >

                <xpath expr="//filter[@string='Status']" position="before">
                    <filter name="category" string="Parent account" domain="[]" context="{'group_by':'parent_id'}"/>
                </xpath>

            </field>
        </record>

The window action

<record id="account_analytic_analysis.action_account_analytic_overdue_all" model="ir.actions.act_window">
            <field name="search_view_id" ref="lawyers_analytic_account.analytic_account_redefine_searchview" />
                <field name="context">{
                'default_type':'contract',
                'search_default_open':1, 
                'search_default_pending':1,
                'default_manager_id':uid,
                'search_default_category':1
                }
            </field>

</record>

When I remove the "search_default_category:1" rule, the error disappears.

How could I restrict that context entry so that it gets applied to Contracts only?