code: func (c *chainView) tip() *blockNode {
  	if len(c.nodes) == 0 {
  		return nil
  	}
  
  	return c.nodes[len(c.nodes)-1]
  }
docs: // tip returns the current tip block node for the chain view.  It will return
  // nil if there is no tip.  This only differs from the exported version in that
  // it is up to the caller to ensure the lock is held.
  //
  // This function MUST be called with the view mutex locked (for reads).