text: 
  var DictKeyNotFound = function(opt_key) {
    if (arguments.length) {
      this.keyWasSupplied = true;
      this.key = opt_key;
    } else {
      this.keyWasSupplied = false;
    }
  };
  
  var DictKeyNotHashable = function(key) {
    this.key = key;
  };
  