• Table Fields
  
• Page Fields
  

You can use this property together with the InitValue Property to make sure that an entry is made in this field. This setting is evaluated for controls and fields during validation. Validation occurs only if the field or control value is updated through the UI, for example, if a value is updated on a page or if a field is updated in a table directly. If a field is updated through application code, then the NotBlank property is not validated.

You can set the NotBlank property to Yes on primary fields in a table. Setting the NotBlank property to Yes on other fields in a table does not cause a red star marking on the UI.

If the NotBlank property is used on other fields than primary fields, the behavior is as follows:

• If the field is blank, and never entered, the page can be closed.
  
• If the field has been entered, and the user tries to enter a blank value, a validation error occurs.
  

Reference