String id cannot be empty in WordPress

How to know it: Open the wp-config.php file and change for this line:

define('WP_DEBUG', false);

to true

define('WP_DEBUG', true);

Problem: Same situation like this using WPML Plugin.

Solution: check database, there are some rows which id is zero. Try to delete all of them.

Then, the table must not have primary key, so set a primary key and set auto increment.

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