• 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. Do not set the NotBlank property to Yes on other fields in a table.

Reference