code: @GwtIncompatible("ByteSource,CharSource")
    public final ByteSource decodingSource(final CharSource encodedSource) {
      checkNotNull(encodedSource);
      return new ByteSource() {
        @Override
        public InputStream openStream() throws IOException {
          return decodingStream(encodedSource.openStream());
        }
      };
    }
docs: Returns a {@code ByteSource} that reads base-encoded bytes from the specified
  {@code CharSource}.