docs: public final String getDirectoryName(final String property) {
      String directory = properties.get(property);
      if (directory == null || directory.isEmpty()){
        return null;
      }
      if (IS_WINDOWS) {
        // Windows swings both ways. If a forward slash was already used, we'll
        // add one at the end if missing. Otherwise use the windows default of \
        if (directory.charAt(directory.length() - 1) == '\\' ||
            directory.charAt(directory.length() - 1) == '/') {
          return directory;
        }
        if (directory.contains("/")) {
          return directory + "/";
        }
        return directory + "\\";
      }
      if (directory.contains("\\")) {
        throw new IllegalArgumentException(
            "Unix path names cannot contain a back slash");
      }
  
      if (directory == null || directory.isEmpty()){
      	return null;
      }
  
      if (directory.charAt(directory.length() - 1) == '/') {
        return directory;
      }
      return directory + "/";
    }