normalized the caster to return always non-null value and fixed minor ui issues

ui/src/components/base/PreviewPopup.svelte

@@ -26,11 +26,19 @@
     }
 </script>
 
-<OverlayPanel bind:this={panel} class="image-preview" popup on:show on:hide>
+<OverlayPanel bind:this={panel} class="image-preview" btnClose={false} popup on:show on:hide>
+    <svelte:fragment slot="header">
+        <div class="overlay-close" on:click|preventDefault={hide}>
+            <i class="ri-close-line" />
+        </div>
+    </svelte:fragment>
+
     <img src={url} alt="Preview" />
 
     <svelte:fragment slot="footer">
-        <a href={url} class="link-hint txt-ellipsis">/../{url.substring(url.lastIndexOf("/") + 1)}</a>
+        <a href={url} title="Download" class="link-hint txt-ellipsis">
+            /../{url.substring(url.lastIndexOf("/") + 1)}
+        </a>
         <div class="flex-fill" />
         <button type="button" class="btn btn-secondary" on:click={hide}>Close</button>
     </svelte:fragment>