rpc: Fail to return undocumented return values

src/qt/test/rpcnestedtests.cpp

@@ -24,7 +24,7 @@ static RPCHelpMan rpcNestedTest_rpc()
             {"arg2", RPCArg::Type::STR, RPCArg::Optional::OMITTED, ""},
             {"arg3", RPCArg::Type::STR, RPCArg::Optional::OMITTED, ""},
         },
-        {},
+        RPCResult{RPCResult::Type::ANY, "", ""},
         RPCExamples{""},
         [](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue {
             return request.params.write(0, 0);