Variable Fetch Records Criteria

Variable Fetch Records Criteria

Trying to create a dynamic list that as users select the various other dropdowns on the form the the list displays all the records from another form that match the selected criteria.  Since not all the dropdowns will be selected I can't just use the standard fetch records method r  =  FormName  [Field1 == input.Field1]; Because it would try to match all the blank dropdowns as part of the criteria.  Is there any way I can create a variable criteria based on which dropdowns are actually in use?