Migrated taxonomy terms error with lastmod cannot be null

Problem/Motivation

Tried to click a button in D8 again and all went down :)
I tried to generate a sitemap added nodetypes. Somehow he doesnt have a value but no details. Can we maybe set a default value?
Or any other ideas how to fix this?

Edit: Taxonomy terms are responsible for this.

Drupal\Core\Database\IntegrityConstraintViolationException: SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'lastmod' cannot be null: INSERT INTO {xmlsitemap} (type, id, language, loc, subtype, access, status, status_override, lastmod, priority, priority_override, changefreq, changecount) VALUES (:db_insert_placeholder_0, :db_insert_placeholder_1, :db_insert_placeholder_2, :db_insert_placeholder_3, :db_insert_placeholder_4, :db_insert_placeholder_5, :db_insert_placeholder_6, :db_insert_placeholder_7, :db_insert_placeholder_8, :db_insert_placeholder_9, :db_insert_placeholder_10, :db_insert_placeholder_11, :db_insert_placeholder_12); Array ( [:db_insert_placeholder_0] => taxonomy_term [:db_insert_placeholder_1] => 11376 [:db_insert_placeholder_2] => de [:db_insert_placeholder_3] => /taxonomy/term/11376 [:db_insert_placeholder_4] => category [:db_insert_placeholder_5] => 1 [:db_insert_placeholder_6] => 1 [:db_insert_placeholder_7] => 0 [:db_insert_placeholder_8] => [:db_insert_placeholder_9] => 0.5 [:db_insert_placeholder_10] => 0 [:db_insert_placeholder_11] => 60 [:db_insert_placeholder_12] => 0 ) in Drupal\Core\Database\Connection->handleQueryException() (Zeile 698 in /www/htdocs/w00bbe43/PRODUCT_DISTRI_5/web/core/lib/Drupal/Core/Database/Connection.php).

Steps to reproduce

Run an incremental taxonomy term migration or drush mim --update your_taxonomy_term_migration

Proposed resolution

Handle NULL values in the changed field of taxonomy terms.

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet