code: @SuppressWarnings("ReturnValueIgnored")
    public ThreadFactoryBuilder setNameFormat(String nameFormat) {
      String.format(nameFormat, 0); // fail fast if the format is bad or null
      this.nameFormat = nameFormat;
      return this;
    }
docs: Sets the naming format to use when naming threads ({@link Thread#setName})
  which are created with this ThreadFactory.
  
  @param nameFormat a {@link String#format(String, Object...)}-compatible
  format String, to which a unique integer (0, 1, etc.) will be supplied
  as the single parameter. This integer will be unique to the built
  instance of the ThreadFactory and will be assigned sequentially. For
  example, {@code "rpc-pool-%d"} will generate thread names like
  {@code "rpc-pool-0"}, {@code "rpc-pool-1"}, {@code "rpc-pool-2"}, etc.
  @return this for the builder pattern