stristr(): Empty needle issue

Hello,
My site automatically down from couple of days. When httpd restart its start working again.
When we checked error logo file is full with these two lines :
PHP Warning: stristr(): Empty needle in /var/www/html/webprod/deskera.co.id/wp-content/plugins/w3-total-cache/lib/Minify/Minify/IgnoredCommentPreserver.php on line 36

[Wed Jun 01 00:40:52 2016] [error] [client 66.249.85.167] PHP Warning: stristr(): Empty needle in /var/www/html/webprod/deskera.co.id/wp-content/plugins/w3-total-cache/lib/Minify/Minify/HTML.php on line 162

https://www.ads-software.com/plugins/w3-total-cache/

Please help me.