Issue with Custom SQL to retrieve row-level results type

There are two types of use cases for the CustomSQL rule. In my case, I want to use a rule of the Custom SQL to retrieve row-level results type. For example: CustomSql "select Name from primary where Age > 18". You can check de detail of this type of rule in the documentation.

However, every time I use a rule of this type, I get the following error: 'No condition provided for rule with non-boolean rule type: CustomSql'. I can't even save the ruleset.

When using rules of the type: CustomSql "select count(*) from primary" between 10 and 20, I don't encounter any issues.

I don't understand why it's giving an error if it's a use case mentioned in the documentation. I've already tried it with different databases but still the same problem... :(