Function convertToColorString

_benchmarks/sample_echarts.js:16639–16642

* @return Never be null/undefined.

(color, defaultColor)

     */

    function convertToColorString(color, defaultColor) {
      defaultColor = defaultColor || 'transparent';
      return isString(color) ? color : isObject(color) ? color.colorStops && (color.colorStops[0] || {}).color || defaultColor : defaultColor;
    }
    /**
     * open new tab
     * @param link url