高德1.4.15版本清除前一个多边形,previousPolygon.setMap(null)或者map.remove(previousPolygon)又或者map.remove([previousPolygon]),之后地图操作都会报错Cannot read properties of null (reading 'Ud')
```javascript
mouseTool.on('draw', function(event) {
var polygon = event.obj; // 获取当前绘制的多边形对象
if(_this.previousPolygon && _this.previousPolygon.getMap()){
_this.map.remove(_this.previousPolygon)
// _this.previousPolygon.setMap(null)
//_this.map.remove([_this.previousPolygon])
}
_this.previousPolygon=polygon
})