fix #15815 (#15817)

tests/stdlib/toptions.nim

@@ -0,0 +1,16 @@
+discard """
+  output: '''{"foo":{"test":"123"}}'''
+"""
+
+import json, options
+
+type
+  Foo = ref object
+    test: string
+  Test = object
+    foo: Option[Foo]
+
+let js = """{"foo": {"test": "123"}}"""
+let parsed = parseJson(js)
+let a = parsed.to(Test)
+echo $(%*a)