In case some warnings are displayed on your website when activating your theme a some plugins, don’t worry. These are PHP warnings, not errors. Unlike errors, warnings won’t break your website. They’re just messages aimed at developers to improve their code.
To hide this message, we suggest you to activate error logging on your website. Please keep WP_DEBUG to true and just paste the following code lines in your wp-config.php file, just before the line that says ‘That’s all, stop editing! Happy blogging.’:
// Enable WP_DEBUG mode
define( 'WP_DEBUG', true );
// Enable Debug logging to the /wp-content/debug.log file
define( 'WP_DEBUG_LOG', true );
// Disable display of errors and warnings
define( 'WP_DEBUG_DISPLAY', false );
@ini_set( 'display_errors', 0 );
More on this in the following topic: Debugging in WordPress
You will still be able to consult the warnings and errors triggered by your website but these won’t appear on your pages anymore.