code: public DirectoryPollerBuilder setThreadName(String name) {
          if (name == null) {
              String message = "Null argument";
              throw new NullPointerException(message);
          }
          threadName = name;
          return this;
      }
docs: Changes the name of the associated polling thread to be equal
  to the given <code>name</code>.
  <p>
  Optional setting. By default each thread is named "DirectoryPoller-{X}",
  where {X} is a sequence number. I.e: "DirectoryPoller-1", "DirectoryPoller-2" etc. etc.
  
  @param name of thread.
  @return {@link DirectoryPollerBuilder}
  @throws NullPointerException if the given argument is null.