Select.php Error: Index Not Defined on Magento 1.9 with PHP 7.1

Does anyone know why I get this error in System.log when running Magento on PHP 7.1?

ERR (3): Notice: Undefined index: label in /home/ronniebergfel/domains/ en line 76

When running on PHP 5.4, I do not get this error. No idea how to solve that?

Sincerely Ronnie