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Fatal error: Uncaught TypeError: Seboettg\CiteProc\Rendering\Name\Names::appendLabel(): Return value must be of type string, null returned in /var/www/ojstest.xyz/ebooksflup/plugins/generic/citationStyleLanguage/lib/vendor/seboettg/citeproc-php/src/Rendering/Name/Names.php:264 Stack trace: #0 /var/www/ojstest.xyz/ebooksflup/plugins/generic/citationStyleLanguage/lib/vendor/seboettg/citeproc-php/src/Rendering/Name/Names.php(223): Seboettg\CiteProc\Rendering\Name\Names->appendLabel() #1 /var/www/ojstest.xyz/ebooksflup/plugins/generic/citationStyleLanguage/lib/vendor/seboettg/citeproc-php/src/Rendering/Group.php(113): Seboettg\CiteProc\Rendering\Name\Names->render() #2 /var/www/ojstest.xyz/ebooksflup/plugins/generic/citationStyleLanguage/lib/vendor/seboettg/citeproc-php/src/Style/Macro.php(86): Seboettg\CiteProc\Rendering\Group->render() #3 /var/www/ojstest.xyz/ebooksflup/plugins/generic/citationStyleLanguage/lib/vendor/seboettg/citeproc-php/src/Rendering/Text.php(290): Seboettg\CiteProc\Style\Macro->render() #4 /var/www/ojstest.xyz/ebooksflup/plugins/generic/citationStyleLanguage/lib/vendor/seboettg/citeproc-php/src/Rendering/Text.php(120): Seboettg\CiteProc\Rendering\Text->renderMacro() #5 /var/www/ojstest.xyz/ebooksflup/plugins/generic/citationStyleLanguage/lib/vendor/seboettg/citeproc-php/src/Rendering/Group.php(113): Seboettg\CiteProc\Rendering\Text->render() #6 /var/www/ojstest.xyz/ebooksflup/plugins/generic/citationStyleLanguage/lib/vendor/seboettg/citeproc-php/src/Rendering/Choose/ChooseIf.php(79): Seboettg\CiteProc\Rendering\Group->render() #7 /var/www/ojstest.xyz/ebooksflup/plugins/generic/citationStyleLanguage/lib/vendor/seboettg/citeproc-php/src/Rendering/Choose/Choose.php(98): Seboettg\CiteProc\Rendering\Choose\ChooseIf->render() #8 /var/www/ojstest.xyz/ebooksflup/plugins/generic/citationStyleLanguage/lib/vendor/seboettg/citeproc-php/src/Rendering/Layout.php(130): Seboettg\CiteProc\Rendering\Choose\Choose->render() #9 /var/www/ojstest.xyz/ebooksflup/plugins/generic/citationStyleLanguage/lib/vendor/seboettg/citeproc-php/src/Rendering/Layout.php(97): Seboettg\CiteProc\Rendering\Layout->renderSingle() #10 /var/www/ojstest.xyz/ebooksflup/plugins/generic/citationStyleLanguage/lib/vendor/seboettg/citeproc-php/src/Style/Bibliography.php(76): Seboettg\CiteProc\Rendering\Layout->render() #11 /var/www/ojstest.xyz/ebooksflup/plugins/generic/citationStyleLanguage/lib/vendor/seboettg/citeproc-php/src/CiteProc.php(137): Seboettg\CiteProc\Style\Bibliography->render() #12 /var/www/ojstest.xyz/ebooksflup/plugins/generic/citationStyleLanguage/lib/vendor/seboettg/citeproc-php/src/CiteProc.php(183): Seboettg\CiteProc\CiteProc->bibliography() #13 /var/www/ojstest.xyz/ebooksflup/plugins/generic/citationStyleLanguage/CitationStyleLanguagePlugin.php(602): Seboettg\CiteProc\CiteProc->render() #14 /var/www/ojstest.xyz/ebooksflup/plugins/generic/citationStyleLanguage/pages/CitationStyleLanguageHandler.php(81): APP\plugins\generic\citationStyleLanguage\CitationStyleLanguagePlugin->getCitation() #15 [internal function]: APP\plugins\generic\citationStyleLanguage\pages\CitationStyleLanguageHandler->get() #16 /var/www/ojstest.xyz/ebooksflup/lib/pkp/classes/core/PKPRouter.php(327): call_user_func() #17 /var/www/ojstest.xyz/ebooksflup/lib/pkp/classes/core/PKPPageRouter.php(249): PKP\core\PKPRouter->_authorizeInitializeAndCallRequest() #18 /var/www/ojstest.xyz/ebooksflup/lib/pkp/classes/core/Dispatcher.php(157): PKP\core\PKPPageRouter->route() #19 /var/www/ojstest.xyz/ebooksflup/lib/pkp/classes/core/PKPApplication.php(429): PKP\core\Dispatcher->dispatch() #20 /var/www/ojstest.xyz/ebooksflup/index.php(21): PKP\core\PKPApplication->execute() #21 {main} thrown in /var/www/ojstest.xyz/ebooksflup/plugins/generic/citationStyleLanguage/lib/vendor/seboettg/citeproc-php/src/Rendering/Name/Names.php on line 264