public static boolean isUnsupported(Endpoint endpoint, SessionProtocol protocol) {
        requireNonNull(endpoint, "endpoint");
        requireNonNull(protocol, "protocol");

        return isUnsupported(key(endpoint, protocol), protocol);
    }
Returns {@code true} if the specified {@link Endpoint} is known to have no support for
the specified {@link SessionProtocol}.
core/src/main/java/com/linecorp/armeria/client/SessionProtocolNegotiationCache.java