plus.android.importClass导入java类失败

离线打包的安卓项目，其中自定义了一个java类，想在uniapp中调用
以下是我的java类

package com.map;  

import android.app.Activity;  
import android.content.Intent;  
import android.os.Bundle;  

public class offlineMap extends Activity {  
    @Override  
    protected void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);  
        startActivity(new Intent(this.getApplicationContext(),  
                com.amap.api.maps.offlinemap.OfflineMapActivity.class));  
    }  

}```  
以下为uniapp中调用

 var main = plus.android.runtimeMainActivity();   
                        var Intent = plus.android.importClass('android.content.Intent');    
                         console.log('intent',Intent);  
                        var MyActivity = plus.android.importClass('com.map.offlineMap');    
                        console.log('MyActivity',MyActivity);  
                        var intent = new Intent(main, MyActivity.class);    
                        main.startActivity(intent); 

然后控制台输出

16:52:57.940 [Vue warn]: Error in v-on handler: "TypeError: Cannot read property 'class' of null"
16:52:58.002 (found at pages/map/history.vue:1)
16:52:58.033 TypeError: Cannot read property 'class' of null

请问这个是什么原因？？