PHP Warning Errors: After upgrade to

hi All,
I’ve upgraded my OJS 2.4.8 to successful. However, I’m keep getting this PHP warning errors" PHP Warning: Declaration of CustomBlockPlugin::getEnabled() should be compatible with BlockPlugin::getEnabled($contextId = NULL) in /var/www/ojs/plugins/generic/customBlockManager/ ". Any where I click, it would come up this error. Is it normal? how do I stop this error ?

many thanks