Make nullable getters use Optional<T> or Option[T]

In many places, the Java WSRequest and WSResponse still use methods which return null:

public interface StandaloneWSRequest {
    String getUsername();

    String getPassword();

    WSAuthScheme getScheme();

    WSSignatureCalculator getCalculator();

    Duration getRequestTimeoutDuration();

    boolean getFollowRedirects();

    String getContentType();
}

And they should return Optional<String> etc where appropriate.

Start by locating the StandaloneWSRequest and WSResponse interfaces and reviewing the listed nullable getters, including getUsername, getPassword, getScheme, getCalculator, getRequestTimeoutDuration, getContentType, and getFollowRedirects. Determine which return types should become Optional or Option[T], then update the affected API consistently; done means nullable getters no longer expose null where the issue specifies.