EMClient.getInstance().getCurrentUser()返回为空是怎么回事

 下面我写的通过EMClient.getInstance().getCurrentUser()替换hxID查找用户但是一直报错为空
private final UserAccountDB mHelper;

public UserInfo getAccountByHxId(String hxId) { 
// 获取数据库对象 
SQLiteDatabase db = mHelper.getReadableDatabase();
 // 执行查询语句 
String sql = "select * from " + UserAccountTable.TAB_NAME + " where " + UserAccountTable.COL_HXID + "=?"; 
Cursor cursor = db.rawQuery(sql, new String[]{hxId});
 UserInfo userInfo = null; 
if(cursor.moveToNext()) {
 userInfo = new UserInfo(); 
// 封装对象 
userInfo.setHxid(cursor.getString(cursor.getColumnIndex(UserAccountTable.COL_HXID))); userInfo.setName(cursor.getString(cursor.getColumnIndex(UserAccountTable.COL_NAME))); userInfo.setNick(cursor.getString(cursor.getColumnIndex(UserAccountTable.COL_NICK))); userInfo.setPhoto(cursor.getString(cursor.getColumnIndex(UserAccountTable.COL_PHOTO))); }
 // 关闭资源 
cursor.close(); 
// 返回数据
 return userInfo; 
}