public static void createHardLinkMult(File parentDir, String[] fileBaseNames,
      File linkDir) throws IOException {
    if (parentDir == null) {
      throw new IOException(
          "invalid arguments to createHardLinkMult: parent directory is null");
    }
    if (linkDir == null) {
      throw new IOException(
          "invalid arguments to createHardLinkMult: link directory is null");
    }
    if (fileBaseNames == null) {
      throw new IOException(
          "invalid arguments to createHardLinkMult: "
          + "filename list can be empty but not null");
    }
    if (!linkDir.exists()) {
      throw new FileNotFoundException(linkDir + " not found.");
    }
    for (String name : fileBaseNames) {
      createLink(linkDir.toPath().resolve(name),
                 parentDir.toPath().resolve(name));
    }
  }
@Test
  public void testCreateHardLinkMultEmptyList() throws IOException {
    String[] emptyList = {};
    
    //test the case of empty file list
    createHardLinkMult(src, emptyList, tgt_mult);
    //check nothing changed in the directory tree
    validateSetup();
  }