Warning: Creating default object from empty value in

I am creating a wordpress site for a customer and a warning message started appearing when I tried to add a new page to the site.

I have tried deactivating all plugins and reverting to basic theme but no joy.

Warning: Creating default object from empty value in /home/customer/www/jeanetteg3.sg-host.com/public_html/wp-admin/includes/post.php on line 736

I would really appreciate any help ??

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