diff --git a/addons/sale/models/product_product.py b/addons/sale/models/product_product.py
index 77ba4fa433f..afcb9a57a14 100644
--- a/addons/sale/models/product_product.py
+++ b/addons/sale/models/product_product.py
@@ -99,7 +99,7 @@ class ProductProduct(models.Model):
 class ProductAttributeCustomValue(models.Model):
     _inherit = "product.attribute.custom.value"
 
-    sale_order_line_id = fields.Many2one('sale.order.line', string="Sales Order Line", required=True, ondelete='cascade')
+    sale_order_line_id = fields.Many2one('sale.order.line', string="Sales Order Line", ondelete='cascade')
 
     _sql_constraints = [
         ('sol_custom_value_unique', 'unique(custom_product_template_attribute_value_id, sale_order_line_id)', "Only one Custom Value is allowed per Attribute Value per Sales Order Line.")