How to use the method that args is List<String> in uel

Flowable Engine
1 
   @Override
    public List<Long> selectUserIdsByPostIds(List<Long> postIds) {
        List<SysUserPost> sysUserPosts = userPostMapper.selectList(
            new LambdaQueryWrapper<SysUserPost>().in(SysUserPost::getPostId, postIds)
        );
        return StreamUtils.toList(sysUserPosts, SysUserPost::getUserId);
    }

  <userTask id="Activity_1y0rge6" name="test" flowable:formKey="static:1831870552204079105" flowable:assignee="${assignee}">
      <incoming>Flow_05gw6bm</incoming>
      <outgoing>Flow_1rsa0pe</outgoing>
      <multiInstanceLoopCharacteristics flowable:collection="${sysUserServiceImpl.selectUserIdsByPostIds(postIds)}" flowable:elementVariable="assignee">
        <completionCondition>${nrOfCompletedInstances/nrOfInstances &gt;= 0.5}</completionCondition>
      </multiInstanceLoopCharacteristics>
    </userTask>

The postIds are fixed. How can I pass the fixed parameters into the UEL expression?