I was creating a dashboard for a sale.order following the 'customizing the existing view' documentation from the odoo Javascript cheatsheet. My problem is I'm able to create and install the application in one instance of odoo(running on port 8069), I can't install it on the production instance(running 8089). The line of code that gives error 'Invalid View definition None' is 

 <attribute name="js_class">sale_dashboard</attribute>

Commenting this line of code can allow me to install the app, but I cannot view any difference in the front end(b/c the dash_board is not added to the view.) I tried to add the dash_board from the front-end by editing the tree view and adding the js_class="dash_board". But even it gives the same error 'Invalid View Definition!'. 

My question is, Is there any other way rather than using the js_class to extend the view?

        <record id="order_tree_dash" model="ir.ui.view">
            <field name="name">sale tree dashboard</field>
            <field name="model">sale.order</field>
            <field name="inherit_id" ref="sale.view_order_tree"/>
            <field name="arch" type="xml">
                <tree position="attributes">
                    <attribute name="js_class">sale_dashboard</attribute>
                </tree>
            </field>
        </record>