PHP Startup: Ignoring replacement of empty string

For some reason I get this when I click on the "configuration" button in the admin page (dashboard)

Any solution for that issue?

@matemolnar88, Not a solution, but... Did you follow up on the suggestion given by the error?

Not yet, so far seems a php version error on the server. If not, then I'll start to debug the things by enable displaying the errors, just like the advice says.