code: function(asUTF8) {
      var result = getRawData(this);
      if (result === null || typeof result === "undefined") {
          return "";
      }
      // if the data is a base64 string, we decode it before checking the encoding !
      if (this.options.base64) {
          result = base64.decode(result);
      }
      if (asUTF8 && this.options.binary) {
          // JSZip.prototype.utf8decode supports arrays as input
          // skip to array => string step, utf8decode will do it.
          result = out.utf8decode(result);
      }
      else {
          // no utf8 transformation, do the array => string step.
          result = utils.transformTo("string", result);
      }
  
      if (!asUTF8 && !this.options.binary) {
          result = out.utf8encode(result);
      }
      return result;
  }
docs: Transform this._data into a string.
  @param {function} filter a function String -> String, applied if not null on the result.
  @return {String} the string representing this._data.