<p></p>
<p><b>@ENT8R</b> commented on this pull request.</p>

<hr>

<p>In <a href="https://github.com/openstreetmap/openstreetmap-website/pull/4203#discussion_r1306403015">app/views/api/users/index.xml.builder</a>:</p>
<pre style='color:#555'>> @@ -1,4 +1,4 @@
 xml.instruct! :xml, :version => "1.0"
 xml.osm(OSM::API.new.xml_root_attributes) do |osm|
-  osm << render(@users)
+  osm << (render(@users) || "")
</pre>
<p dir="auto">I think so, see also <a class="issue-link js-issue-link" data-error-text="Failed to load title" data-id="441428833" data-permission-text="Title is private" data-url="https://github.com/openstreetmap/openstreetmap-website/issues/2223" data-hovercard-type="pull_request" data-hovercard-url="/openstreetmap/openstreetmap-website/pull/2223/hovercard?comment_id=300065590&comment_type=review_comment" href="https://github.com/openstreetmap/openstreetmap-website/pull/2223#discussion_r300065590">#2223 (comment)</a><br>
If the set is empty, rendering fails with <code class="notranslate">ActionView::Template::Error: no implicit conversion of nil into String</code>, because <code class="notranslate">render()</code> returns nil in that case and trying to concatenate nil with an existing string will fail (but concatenating an empty string with another string works).<br>
Regarding the JSON version, this is not an issue because no strings are concatenated there.</p>

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