code: public String add(String extension, String mimeType) {
  		Mapping previous = this.map.put(extension, new Mapping(extension, mimeType));
  		return (previous != null) ? previous.getMimeType() : null;
  	}
docs: Add a new mime mapping.
  @param extension the file extension (excluding '.')
  @param mimeType the mime type to map
  @return any previous mapping or {@code null}