// NOTE: There's java.nio.charset.MalformedInputException and sun.io.MalformedInputException
                if (e.getClass().getName().endsWith("MalformedInputException")) {
                    msg = "Some input bytes do not match the file encoding.";
                } else {
                    msg = e.getClass().getSimpleName();
                }
            }
            problems.add(
                    Severity.FATAL,

    public Optional<String> getString(URI relativeSource, Charset charset) {
        requireNonNull(charset, "charset is null");
        Optional<byte[]> data = getBytes(relativeSource);
        return data.map(bytes -> new String(bytes, charset));
    }

    @Override
    public void put(Path source, URI relativeTarget) {
        requireNonNull(source, "source is null");
        requireNonNull(relativeTarget, "relativeTarget is null");