LinearGradient = function (x, y, x2, y2, colorStops, globalCoord) {
	        // Should do nothing more in this constructor. Because gradient can be
	        // declard by `color: {type: 'linear', colorStops: ...}`, where
	        // this constructor will not be called.

	        this.x = x == null ? 0 : x;

	        this.y = y == null ? 0 : y;

	        this.x2 = x2 == null ? 1 : x2;

	        this.y2 = y2 == null ? 0 : y2;

	        // Can be cloned
	        this.type = 'linear';

	        // If use global coord
	        this.global = globalCoord || false;

	        Gradient.call(this, colorStops);
	    }
key: componentType
value:  Component model list, can not be null.
@type {Object.<string, Array.<module:echarts/model/Model>>}
@readOnly