Missing to show in editor where is problem

public static void main(String[] args)

{ List<Integer> z = List.of(1,2,3); z.stream() .map(SandboxTemp1::ou) .toString(); }

private static int ou(String o)

{ return 0; }

There is missing to be shown as error on such line.

It is seen as issue in action items and red indicator in tab next name of file, but no issue shown in editor itself.

In actions items you can see:
Error incompatible types: invalid method reference incompatible types: java.lang.Integer cannot be converted to java.lang.String ... :23

This is not one case, but this happens for different types so not only that one from example.