wpf imagesource bad trigger

I want to cre开发者_JS百科ate a data trigger in pure xaml (as in, no events or convertors or any bhind code), that will trigger if an image source doesn't have an image. For example I have an image browser and image preview, and I want to do something if the the browser selected a file that isn't an image.

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Is it mandatory using Data Trigger ? Can't you just set de Property Trigger in style ?

Something like :

<Style.Triggers>
<Trigger Property="Source" Value="">
  Something here...
</Trigger>

Tell me if it's not the behaviour you expect