Remove trailing slash in path created by the ImageViewHelper - typo3

Question

I am trying to add CSS code to a template file using Fluid. I want to render a background-image uploaded at /fileadmin/user_upload/foo.jpg
However, {images.0.url} returns the path /fileadmin/user_upload/foo.jpg/
with a trailing slash, which then of course throws the following error:
TYPO3Fluid\Fluid\Core\ViewHelper\Exception
Supplied file object type TYPO3\CMS\Core\Resource\Folder for must be File or FileReference.
How can I remove the trailing slash from the path?
Below, the relevant code snippet is shown. Please note that v:format.prepend is just used for debugging purposes here and has no effect on the issue.
<f:section name="Header">
<v:page.resources.fal table="pages" field="media" uid="{page.uid}" as="images" slide="-1" >
<v:asset.style name="header">
header#header <f:format.raw>{</f:format.raw>
background-image: url(<f:uri.image src="{v:format.prepend(add: '', subject: '{images.0.url}')}" treatIdAsReference="1" />)
<f:format.raw>}</f:format.raw>
</v:asset.style>
</v:page.resources.fal>
<f:render section="Default" partial="DefaultHeader" arguments="{_all}"/>
</f:section>

Answer 1

Do you think about the following?
You can remove the wrapping vhs ViewHelper and access the first media directly.
<v:asset.style name="header">
header#header <f:format.raw>{</f:format.raw>
background-image: url({f:uri.image(image:data.media.0})
<f:format.raw>}</f:format.raw>
</v:asset.style>

Answer 2

Faced a similar problem. Solved it by using absolute URLs of images. In my case it was (get URL):
<f:variable name="mediaUrl">{f:uri.image(image: mediaObject, treatIdAsReference: 1, absolute : 1)}</f:variable>
Later using URL as source:
data-src="{f:uri.image(src: mediaUrl, treatIdAsReference: 0)}"
I was switching sources between a provided obj and static resource uri based on condition, so this was necessary and came handy.