PHP Simple HTML DOM, Notice: Trying to get property of non-object

I am getting Notice: Trying to get property of non-object at:

$var = trim($article->find('span[id$=qty]', 0)->innertext);

$article is a 开发者_如何学运维simple_html_dom() object.

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Maybe span[id$=qty] evaluates to null; means: no node was found.