@Override
    public Throwable fillInStackTrace() {
        if (Flags.verboseExceptionSampler().isSampled(getClass())) {
            return super.fillInStackTrace();
        }
        return this;
    }
Returns the actual {@link SessionProtocol}.

@return the actual {@link SessionProtocol}, or {@code null} if failed to determine the protocol.
core/src/main/java/com/linecorp/armeria/client/SessionProtocolNegotiationException.java