index.js
function end() {
    try {
      this.queue(transformCss(filePath, data, opts));
    } catch(err) {
      this.emit("error", new Error(err));
    }

    this.queue(null);
  }
function end() {
    try {
      this.queue(transformCss(filePath, data, opts));
    } catch(err) {
      this.emit("error", new Error(err));
    }

    this.queue(null);
  }
Implementation of through interface.