code: private String getExtension(String fileName) {
  		if (fileName == null) {
              return null;
          }
  
  		String ext = null;
  		int i = fileName.lastIndexOf('.');
  
  		if (i > 0 && i < fileName.length() - 1) {
  			ext = fileName.substring(i + 1).toLowerCase();
  		}
  		return ext;
  	}
docs: Return the extension of the filename
  
  @param fileName
  that should be inputed
  @return file extension or null