Fixed nitpick comment

Author: tomasherceg

src/Framework/Framework/Routing/DotvvmRouteTable.cs

@@ -312,18 +312,19 @@ IEnumerator IEnumerable.GetEnumerator()
         [return: NotNullIfNotNull(nameof(appendedPath))]
         private string? CombinePath(string? prefix, string? appendedPath)
         {
-            if (string.IsNullOrEmpty(prefix))
+            if (appendedPath == null)
             {
-                return appendedPath;
+                // NB: if you are adding presenter route inside a group, we ignore the group's virtual path because presenter routes have VirtualPath = null
+                return null;
             }
 
-            if (appendedPath == null)
+            if (string.IsNullOrEmpty(prefix))
             {
-                return null;
+                return appendedPath;
             }
-            else if (appendedPath == string.Empty)
+            else if (string.IsNullOrEmpty(appendedPath))
             {
-                return prefix ?? string.Empty;
+                return prefix;
             }
 
             return $"{prefix}/{appendedPath}";