How to fix the "Strict Standards: Declaration of TGM_Bulk_Installer_Skin" error?

The combination of an outdated theme and a PHP conversion can result in the following error message:

Strict Standards: Declaration of TGM_Bulk_Installer_Skin::before() should be compatible with Bulk_Upgrader_Skin::before($title = '') in /wp-content/themes/xxx/inc/class-tgm-plugin-activation.php on line 1893
Strict Standards: Declaration of TGM_Bulk_Installer_Skin::after() should be compatible with Bulk_Upgrader_Skin::after($title = '') in /wp-content/themes/xxx/inc/class-tgm-plugin-activation.php on line 1893

Solution: To do this, two lines of code must be changed, but the line number can be different, here you should use the search function.

In line 1977 you change the code

public function before() {


public function before( $title = '' ) {

And in line 1999:

public function after() {


public function after( $title = '' ) {
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