PbootCMS文章列表没有缩略图时也不显示默认图片怎么办

{pboot:list scode={sort:scode}}
<li class="note-li">
<a href="[list:link]" title="[list:title]">
<div class="flex-column">
{pboot:if('[list:isico]'=='1')}
<div class="img-box">
<img src="[list:ico]" alt="[list:title]">
</div>
{/pboot:if}
<div class="text-box">
<h4>[list:title]</h4>
<p class="intro hidden-sm">[list:content drophtml=1 dropblank=1 lencn=120]</p>
<p><span><i class="fa fa-clock-o" aria-hidden="true"></i> [list:date style=Y-m-d]</span><span><i class="fa fa-eye" aria-hidden="true"></i> list:visits 浏览</span><span><i class="fa fa-thumbs-up" aria-hidden="true"></i> list:likes 点赞</span></p>
</div>
</div>
</a>
</li>
{/pboot:list}

{pboot:if('list:isico'=='1')}
<div class="img-box">
<img src="[list:ico]" alt="[list:title]">
</div>
{/pboot:if}