code: public String getMeta(String key) {
  		String value = manifest.getMainAttributes().getValue(key);
  		if (value == null) {
  			throw new InvalidFilesArchiveException("Missing |%s| attribute from manifest.", key);
  		}
  		return value;
  	}
docs: Get string value from files archive meta data. Meta data was added into archive by
  {@link FilesOutputStream#putMeta(String, Object)}.
  
  @param key meta data key.
  @return meta data value.
  @throws InvalidFilesArchiveException if requested meta data key does not exists.