docs: @Pure
  	public static URL dirname(File filename) {
  		if (filename == null) {
  			return null;
  		}
  		String parent = fromFileStandardToURLStandard(filename.getParent());
  		try {
  			if (parent == null || "".equals(parent)) { //$NON-NLS-1$
  				if (filename.isAbsolute()) {
  					return null;
  				}
  				return new URL(URISchemeType.FILE.name(), "", CURRENT_DIRECTORY); //$NON-NLS-1$
  			}
  			// Treat Windows specific.
  			if (Pattern.matches("^" + URL_PATH_SEPARATOR + "?[a-zA-Z][:|]$", parent)) { //$NON-NLS-1$ //$NON-NLS-2$
  				parent += URL_PATH_SEPARATOR;
  			}
  			return new URL(URISchemeType.FILE.name(), "", parent); //$NON-NLS-1$
  		} catch (MalformedURLException exception) {
  			return null;
  		}
  	}