>>> [!note] Migrated issue <!-- Drupal.org comment --> <!-- Migrated from issue #3563266. --> Reported by: [joseph.olstad](https://www.drupal.org/user/1321830) Related to !154 !160 >>> <h3 id="summary-problem-motivation">Problem/Motivation</h3> <p>Upgrading from a fresh book 2.0.x installation.</p> <p>Getting this error:<br> <code>TypeError: Cannot access offset of type string on string in book_post_update_allowed_child_type_default6</code></p> <p>Stack of errors:</p> <pre> [error] TypeError: Cannot access offset of type string on string in book_post_update_allowed_child_type_default6() (line 148 of /www/web/modules/contrib/book/book.post_update.php) #0 /www/vendor/drush/drush/src/Commands/core/UpdateDBCommands.php(291): book_post_update_allowed_child_type_default6(Array)<br>&gt; #1 /www/vendor/drush/drush/includes/batch.inc(257): Drush\Commands\core\UpdateDBCommands::updateDoOnePostUpdate('book_post_updat...', Array)<br>&gt; #2 /www/vendor/drush/drush/includes/batch.inc(204): _drush_batch_worker()<br>&gt; #3 /www/vendor/drush/drush/includes/batch.inc(75): _drush_batch_command('1')<br>&gt; #4 /www/vendor/drush/drush/src/Commands/core/UpdateDBCommands.php(145): drush_batch_command('1')<br>&gt; #5 [internal function]: Drush\Commands\core\UpdateDBCommands-&gt;process('1', Array)<br>&gt; #18 {main}.<br>&gt; TypeError: Cannot access offset of type string on string in /www/web/modules/contrib/book/book.post_update.php on line 148 #0 /www/vendor/drush/drush/src/Commands/core/UpdateDBCommands.php(291): book_post_update_allowed_child_type_default6(Array)<br>&gt; #1 /www/vendor/drush/drush/includes/batch.inc(257): Drush\Commands\core\UpdateDBCommands::updateDoOnePostUpdate('book_post_updat...', Array)<br>&gt; [warning] Drush command terminated abnormally.<br><br>In ProcessBase.php line 171:<br><br>Unable to decode output into JSON: Syntax error<br><br>TypeError: Cannot access offset of type string on string in book_post_update_allowed_child_type_default6() (line 148 of /www/html/modules/contrib/book/book.post_update.php).</pre><h4 id="summary-steps-reproduce">Steps to reproduce</h4> <p>Install book 2.0.x with this configuration:<br> <code>book.settings.yml</code></p> <pre>allowed_type_book: 1<br>block:<br>&nbsp; navigation:<br>&nbsp;&nbsp;&nbsp; mode: 'all pages'<br>child_type_book: book</pre><p> Then upgrade to book 3.0.x</p> <p>Then observe bug.</p> <h3 id="summary-proposed-resolution">Proposed resolution</h3> <p>See code in merge request</p> <h3 id="summary-remaining-tasks">Remaining tasks</h3> <p>Review code in merge request</p> <h3 id="summary-ui-changes">User interface changes</h3> <p>Allows upgrades without crashing</p> <h3 id="summary-api-changes">API changes</h3> <p>See merge request</p> <h3 id="summary-data-model-changes">Data model changes</h3> <p>See merge request</p>