I just tried both cases in the rules class and both do not catch that the field is actually empty.

if (mmType.IsEmpty(first_Name, true))

if (mmType.IsEmpty(first_Name, false))

All I do is bring up the form, choose, in my case, a Project, then go to the Properties page and in a Required field I select the existing letters WFBCI and delete them, not knowing this is a 10 character field and there are still 5 spaces remaining. I then click the Save button and the changes save with the blank field. I put in the .trim() and the rule catches the above and indicates it is a required field.

if (mmType.IsEmpty(first_Name.trim()))