Unable to export database via phpMyAdmin in Plesk: Argument 5 passed to PhpMyAdmin\Export::getFilenameAndMimetype() must be of the type string, null given

Symptoms

Unable to export database via phpMyAdmin:

CONFIG_TEXT: Argument 5 passed to PhpMyAdmin\Export::getFilenameAndMimetype() must be of the type string, null given, called in /opt/psa/admin/htdocs/domains/databases/phpMyAdmin/export.php on line 380

The following warning is shown while accessing "Export" tab:

PLESK_WARN: Warning: a form on this page has more that 1000 fields. On submission, some of this fields might be ignored, due to PHP's max_input_vars configuration.

Cause

Huge amount of tables in database: more than 1000, it is too large for Plesk PHP engine to process them.

Resolution

For Linux:

Increase the memory_limit, max_input_vars parameters in Plesk PHP according to these instructions.

For Windows:

1. Connect to the server via RDP
2. Open C:\Program Files (x86)\Plesk\admin\conf\php.ini
3. Find line like max_input_vars = <number> (add it if not present)
4. Set <number> to a number larger than default of 1000, e.g. 1500 or 2000