<?php
defined('TYPO3_MODE') or die();

// Default TypoScript
\TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addStaticFile($_EXTKEY, 'Configuration/TypoScript', 'Bootstrap Package');

<?php
defined('TYPO3_MODE') or die();

/***************
 * Default TypoScript
 */
\TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addStaticFile(
    'bootstrap_package',
    'Configuration/TypoScript',
    'Bootstrap Package'
);

Use string to identify bootstrap_package for adding static template
[BUGFIX] Use string to identify bootstrap_package for adding static template
