Problem/Motivation
There is currently no way to remove an empty destination property from a Row once it has been added. This limits the ability of migration event subscribers to alter the outcome of a migration update.
Steps to reproduce
Create a migration that will null out the contents of a field for a particular entity. Use the PRE_ROW_SAVE event to attempt to undo that, and see that the Row class does not provide a public method to accomplish this.
Proposed resolution
Add public methods to the Row class.
Remaining tasks
None
User interface changes
None
Introduced terminology
None
API changes
New methods added to \Drupal\migrate\Row.
Data model changes
None
Release notes snippet
None
