Uncaught Error: Call to a member function get_slider_language()

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I'm attempting to move my wordpress sites over to Google Cloud, I've moved two successfully with revslider - the third had a bloated database and I needed to trim some fat to get it in.

I'm now getting the following error when trying to view a slide from any of the front-end pages.

Fatal error: Uncaught Error: Call to a member function get_slider_language() on null in /var/www/rr/wp-content/plugins/revslider/includes/output.class.php:675 Stack trace: #0 /var/www/rr/wp-content/plugins/revslider/includes/output.class.php(634): RevSliderOutput->add_slider_base() #1 /var/www/rr/wp-content/plugins/revslider/revslider.php(96): RevSliderOutput->add_slider_to_stage('new_home', '', '', '', '') #2 /var/www/rr/wp-includes/shortcodes.php(343): rev_slider_shortcode(Array, '', 'rev_slider') #3 [internal function]: do_shortcode_tag(Array) #4 /var/www/rr/wp-includes/shortcodes.php(218): preg_replace_callback('/\\[(\\[?)(rev_sl...', 'do_shortcode_ta...', '[rev_slider sli...') #5 /var/www/rr/wp-content/plugins/js_composer/include/helpers/helpers.php(240): do_shortcode('[rev_slider sli...') #6 /var/www/rr/wp-content/plugins/js_composer/include/templates/shortcodes/vc_column.php(94): wpb_js_remove_wpautop('[rev_slider sli...') #7 /var/www/rr/wp-content/plugins/js_composer/include/classes/shortcodes/core/class-wpbakerys in /var/www/rr/wp-content/plugins/revslider/includes/output.class.php on line 675

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I've attempted the following steps to no avail.

  1. Switched theme.
  2. Disabled all plugins.
  3. Deleted all slides and attempted with a freshly made slide.
  4. Updated all plugins, including deleting Slider Revolution entirely and reinstalling the latest version.
  5. I removed some language packs from the VM in an attempt to claw back some space and thought that might've been it - but reinstalling with apt-get -y install "check-language-support -l en" doesn't seem to have helped.
  6. Updated to PHP 7.4.8

I'm using a Google Cloud VM with OpenLiteSpeed, and MySQL+Redis. I changed the only relevant option I could see in Slider Revolution Global Config from using default as the language to en. The slide works as expected in preview mode within the admin panel.

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1 Answers

This is caused by what appears to be a bug in the Revolution Slider plugin, at least as of v6.2.21 (and it doesn't appear to have been fixed since). In revslider/includes/output.class.php:678 it calls

$lang = $rs_wmpl->get_slider_language($this->slider);

but if the WPML plugin is not installed, then $rs_wmpl is null.

Until they fix it you can hack the plugin to check for null, e.g.,

    //set slider language
    if($this->get_preview_mode() == false && !empty($rs_wmpl)){
        $lang = $rs_wmpl->get_slider_language($this->slider);
        $this->change_language($lang);
    }

Edit: This bug doesn't reproduce under ordinary page loads, but does reproduce when loading the site under WP-CLI, e.g., via wp profile. Suspect it has something to do with the way global variables are handled in that case.

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