Use of conditional merge tag in the content of the advanced post creation feed

I have an optional file upload field that I would like to populate into an image tag in a generated post.

Hardcoding the img tag works fine.

<img src="* my image merge tag here *" />

But this still creates the tag when the user doesn’t provide an image.

I tried to use the conditional merge tag in the body of the content but the conditional tag just appeared in the post as full text with only the image tag replaced.

[gravityforms action="conditional" merge_tag="* my image merge tag here *" condition="isnot" value=""]
<img src="* my image merge tag here *" />
[/gravityforms]

Am I doing something wrong or is there no way to do conditions in the body of the post feed content ?