Error message

• Warning: Trying to access array offset on value of type bool in include() (line 90 of /home/gdmmd/public_html/old.gdm.md/sites/all/themes/lgbt/node--book.tpl.php).
• Warning: Trying to access array offset on value of type null in include() (line 90 of /home/gdmmd/public_html/old.gdm.md/sites/all/themes/lgbt/node--book.tpl.php).