private @NotNull String filterAlreadyRegisteredExtensions(@NotNull String semicolonDelimited) {
    StringTokenizer tokenizer = new StringTokenizer(semicolonDelimited, FileTypeConsumer.EXTENSION_DELIMITER, false);
    StringBuilder builder = null;
    while (tokenizer.hasMoreTokens()) {
      String extension = tokenizer.nextToken().trim();
      if (pendingAssociations.findByExtension(extension) == null && getFileTypeByExtension(extension) == UnknownFileType.INSTANCE) {
        if (builder == null) {
          builder = new StringBuilder();
        }
        else if (!builder.isEmpty()) {
          builder.append(FileTypeConsumer.EXTENSION_DELIMITER);
        }
        builder.append(extension);
      }
    }
    return builder == null ? "" : builder.toString();
  }
private @NotNull String filterAlreadyRegisteredExtensions(@NotNull String semicolonDelimited)