code: public <R> R executeAndQuery(ContextCommand<ROOT, R> cmd) {
          return Politician.beatAroundTheBush(() -> this.prevayler.execute(new InternalTransaction<>(cmd)));
      }
docs: Perform command on system.
  <p>
  Inside command can be any code doing any changes. Such changes are
  guaranteed to be preserved (if only command ended without exception).
  
  @param cmd