- <button string="Sent by Email" icon="gtk-ok" type="object" name="action_invoice_sent" attrs="{'invisible': ['|', ('sent','=', True), ('state', '!=', 'paid')]}"/>
+ <button string="Sent by Email" type="object" name="action_invoice_sent" attrs="{'invisible': ['|', ('sent','=', True), ('state', '!=', 'paid')]}"/>