src/utils/rbt.js
function RBTSentinel() {
  this.key = null;
  this.value = null;
  this.color = BLACK;
  this.parent = null;
  this.left = null;
  this.right = null;
}
function RBTSentinel() {
  this.key = null;
  this.value = null;
  this.color = BLACK;
  this.parent = null;
  this.left = null;
  this.right = null;
}
function RBTSentinel ( ) { this . key = null ; this . value = null ; this . color = BLACK ; this . parent = null ; this . left = null ; this . right = null ; }
RBT Sentinel Node
@constructor
@ignore
@property {null} key
@property {null} value
@property {Number} [color=BLACK]
@property {null} parent
@property {null} left
@property {null} right
RBT Sentinel Node