What i would do to check if an attribute value is empty, for example in a password form, is to create a boolean variable and then a decision step with a small expression like
Based on the Boolean True or False you could input a new activity. Don’t forget to add the object as paramater and retrieve the object first though!
As far as I am aware there is no way to auto-check all of the attributes in a microflow.
You can consider adding the validations on entity level in your domain model but you’ll still have to do it for all of the attributes.
Documentation: Set Up Data Validation - Studio Pro 9 How-to's | Mendix Documentation
If you don’t want to validate on entity level, I suggest you download the CommunityCommons module and use the ‘IsNotEmptyString’ Rule to check each of the attributes.