Failing self containing hello world snippet

UltiSnips/snippets.snippets

@@ -4,3 +4,9 @@ $4
 `!p snip.rv = "endsnippet"`
 $0
 endsnippet
+
+snippet helloworld "A simple hello world snippet" b
+${0:`!p
+if not snip.c:
+	snip.rv = f'snippet helloworld "A simple hello world snippet" b\n{t[0]}\nendsnippet'`}
+endsnippet