docs: function(start, len) {
          if ('number' === typeof start) {
  
            if ((start < 0) || (start >= get(this, 'length'))) {
              throw new EmberError(OUT_OF_RANGE_EXCEPTION);
            }
  
            // fast case
            if (len === undefined) len = 1;
            this.replace(start, len, EMPTY);
          }
  
          return this;
        }