Error processing MakePdfBook command:

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

Error was:
OutOfBoundsException: There is no such book as "Youth_Martial_Handbook" 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('Youth_Martial_H...')
#1 /var/www/html/extensions/MakePdfBook/src/SpecialMakePdfBook.php(35): MediaWiki\Extension\MakePdfBook\SpecialMakePdfBook->servePdf('Youth_Martial_H...', Array)
#2 /var/www/html/includes/specialpage/SpecialPage.php(728): MediaWiki\Extension\MakePdfBook\SpecialMakePdfBook->execute('render/Youth_Ma...')
#3 /var/www/html/includes/specialpage/SpecialPageFactory.php(1621): MediaWiki\SpecialPage\SpecialPage->run('render/Youth_Ma...')
#4 /var/www/html/includes/MediaWiki.php(357): MediaWiki\SpecialPage\SpecialPageFactory->executePath('MakePdfBook/ren...', Object(RequestContext))
#5 /var/www/html/includes/MediaWiki.php(960): MediaWiki->performRequest()
#6 /var/www/html/includes/MediaWiki.php(613): MediaWiki->main()
#7 /var/www/html/index.php(50): MediaWiki->run()
#8 /var/www/html/index.php(46): wfIndexMain()
#9 {main}