Error processing MakePdfBook command:

Encountered error while attempting to execute MakePdfBook command \'render\' for target \'Armored_Steel_Combat_Handbook_Wiki_PDF_version\'.

Error was:
OutOfBoundsException: There is no such book as "Armored_Steel_Combat_Handbook_Wiki_PDF_version" in /var/www/html/extensions/MakePdfBook/src/BookSet.php:74
Stack trace:
#0 /var/www/html/extensions/MakePdfBook/src/SpecialMakePdfBook.php(192): MediaWiki\Extension\MakePdfBook\BookSet->getBook('Armored_Steel_C...')
#1 /var/www/html/extensions/MakePdfBook/src/SpecialMakePdfBook.php(35): MediaWiki\Extension\MakePdfBook\SpecialMakePdfBook->servePdf('Armored_Steel_C...', Array)
#2 /var/www/html/includes/specialpage/SpecialPage.php(728): MediaWiki\Extension\MakePdfBook\SpecialMakePdfBook->execute('render/Armored_...')
#3 /var/www/html/includes/specialpage/SpecialPageFactory.php(1717): MediaWiki\SpecialPage\SpecialPage->run('render/Armored_...')
#4 /var/www/html/includes/actions/ActionEntryPoint.php(504): MediaWiki\SpecialPage\SpecialPageFactory->executePath('MakePdfBook/ren...', Object(MediaWiki\Context\RequestContext))
#5 /var/www/html/includes/actions/ActionEntryPoint.php(146): MediaWiki\Actions\ActionEntryPoint->performRequest()
#6 /var/www/html/includes/MediaWikiEntryPoint.php(200): MediaWiki\Actions\ActionEntryPoint->execute()
#7 /var/www/html/index.php(58): MediaWiki\MediaWikiEntryPoint->run()
#8 {main}