i've experienced the same issue but i'm not sure if my fix is good
the problem is always the same fields declared as NOT NULL needs a valus

my dirty fix on line 232 of libraries\cms\helper\tags.php i've added

// Initialize some variables.
                $db = JFactory::getDbo();
                $query = $db->getQuery(true);
            $tagTable->checked_out_time = $query->currentTimestamp();
            $tagTable->publish_up = $query->currentTimestamp();
            $tagTable->publish_down = $query->currentTimestamp();
            $tagTable->params = '{}';
            $tagTable->metadesc= ' ';
            $tagTable->metakey= ' ';
            $tagTable->metadata= ' ';
            $tagTable->images= ' ';
            $tagTable->urls= ' ';

This is a very dirty fix ^.^

I think this should be done in the table check rather than in the helper. Urls and images as per other fields should be empty json encoded (like the params is). But for the principle

closed as we have a PR #6314