@Override
  public @Nullable Object get(File file, String attribute) {
    Object value = file.getAttribute("user", attribute);
    if (value instanceof byte[]) {
      byte[] bytes = (byte[]) value;
      return bytes.clone();
    }
    return null;
  }
Attribute provider that provides the {@link UserDefinedFileAttributeView} ("user"). Unlike most
other attribute providers, this one has no pre-defined set of attributes. Rather, it allows
arbitrary user defined attributes to be set (as {@code ByteBuffer} or {@code byte[]}) and read
(as {@code byte[]}).

@author Colin Decker
jimfs/src/main/java/com/google/common/jimfs/UserDefinedAttributeProvider.java