@Nullable
    @Override
    public <T> T unwrap(Object client, Class<T> type) {
        final T unwrapped = super.unwrap(client, type);
        if (unwrapped != null) {
            return unwrapped;
        }

        if (!(client instanceof AbstractStub)) {
            return null;
        }

        final Channel ch = ((AbstractStub<?>) client).getChannel();
        if (!(ch instanceof Unwrappable)) {
            return null;
        }

        return ((Unwrappable) ch).as(type);
    }
Adds the {@link GrpcWebTrailersExtractor} if the specified {@link SerializationFormat} is a gRPC-Web and
{@link RetryingClient} exists in the {@link ClientDecoration}.
grpc/src/main/java/com/linecorp/armeria/internal/client/grpc/GrpcClientFactory.java