code: public static void unpack(File zip, final File outputDir, Charset charset) {
      unpack(zip, outputDir, IdentityNameMapper.INSTANCE, charset);
    }
docs: Unpacks a ZIP file to the given directory using a specific Charset
  for the input file.
  
  <p>
  The output directory must not be a file.
  
  @param zip
  input ZIP file.
  @param outputDir
  output directory (created automatically if not found).
  
  @param charset
  charset used to unpack the zip file