Set a field to a specific value if your items are missing information
Add content to a gender field for Google Shopping
Use the set to value action to add missing information to your items or to change the information. For example, for a Google Shopping feed you need a gender field, which you need to set to either "male", "female" or "unisex".
This rule will set the gender field to "male" for all items that have a product_type containing the word "men".