Hello Jace,
Not enough information. What do you mean by EMPTY?
Are you saying that the field in a row can be NULL?
By default, in OutSystems tables, the only way to a NULL to appear as the value of a field is if you are doing a LEFT JOIN and there is no match in the table being joined. In this case, during the execution of the query, the fields of that entity for the lines were there isn't match will be NULL.
In this case, if you want to filter out those lines, use the IS NOT NULL operator on the entity id in the WHERE clause.
If you are just talking about records that where inserted without some values, than you must filter against the default value, the one you provided in the Default property of the attribute, or the data type default values, as when inserting records, the platform will give values if you don't provide one, like 0 to integers, "" to text, False to booleans, etc.
Cheers
Eduardo Jauch