code: public void close() {
          Politician.beatAroundTheBush(() -> {
              if (this.prevayler != null) {
                  this.optionalSnapshot();
                  this.prevayler.close();
                  this.prevayler = null;
              }
          });
      }
docs: Close system.
  <p>
  This couses snapshot of system to be done. After this operation
  Controller should be no more usable.