code: public static String concatPathAndFilename(final String path, final String filename, final String separator) {
  
          checkNotNull("filename", filename);
          checkNotNull("separator", separator);
          checkNotEmpty("separator", separator);
  
          if (path == null) {
              return filename;
          }
          final String trimmedPath = path.trim();
          if (trimmedPath.length() == 0) {
              return filename;
          }
          final String trimmedFilename = filename.trim();
          if (trimmedPath.endsWith(separator)) {
              return trimmedPath + trimmedFilename;
          }
          return trimmedPath + separator + trimmedFilename;
  
      }
docs: Concatenate a path and a filename taking <code>null</code> and empty string values into account.
  
  @param path
  Path - Can be <code>null</code> or an empty string.
  @param filename
  Filename - Cannot be <code>null</code>.
  @param separator
  Separator for directories - Can be <code>null</code> or an empty string.
  
  @return Path and filename divided by the separator.