question: public static void onOperatorError ( BiFunction < ? super Throwable , Object , ? extends Throwable > f ) { log . info ( "Hooking new default : onOperatorError" ) ; onOperatorErrorHook = Objects . requireNonNull ( f , "onOperatorErrorHook" ) ; }
target:  Override global operator error mapping which by default add as suppressed exception either data driven exception or error driven exception.