<field name="default_code" attrs="{'invisible': [('product_variant_count', '>', 1)]}"/>
</field>
<xpath expr="//page[@string='Sales']" position="after">
<field name="default_code" attrs="{'invisible': [('product_variant_count', '>', 1)]}"/>
</field>
<xpath expr="//page[@string='Sales']" position="after">