Profile - Change "Value cannot be null" validation message to be user-friendly

[pjmonks]

Describe the bug
If editing a profile which has mandatory fields, if a user left out a field value and then validates the profile then a validation message "Value cannot be null" is returned.

Expected behavior
This is correct. However, from a user experience perspective, the validation message looks a bit too technical and unfriendly.

The suggested improvement is to update mdm-plugin-profile/grails-app/i18n/messages.properties with more user-friendly messages. For example:

"This field cannot be empty"

Screenshots

[olliefreeman]

please check mdm-application-build does NOT override the appropriate message, and if so, also update MAB