From 9817b4963af035a0eb4951f70d566821e3e1cc48 Mon Sep 17 00:00:00 2001
From: Richard Bowman <richard.bowman@cantab.net>
Date: Fri, 1 Dec 2023 21:14:24 +0000
Subject: [PATCH] Handle missing Thing better in thingFormUrl

We now give a helpful error message if the Thing is not found,
rather than returning null. There's an argument to return
`undefined` instead of raising an error, returning undefined
is the default behaviour.
---
 webapp/src/wot-client.js | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/webapp/src/wot-client.js b/webapp/src/wot-client.js
index edfb5709..b1aa58d6 100644
--- a/webapp/src/wot-client.js
+++ b/webapp/src/wot-client.js
@@ -71,7 +71,10 @@ export const wotStoreModule = {
     ) => {
       // Find the URL for a particular operation
       let td = state.thingDescriptions[thing];
-      if (!td) return null;
+      if (!td) {
+        if (allowUndefined) return undefined;
+        throw `Could not find form for ${affordanceType} ${thing}/${affordance} with op ${op}`;
+      }
       let affordances = td[affordanceType];
       let href = findFormHref(affordances[affordance], op);
       if (href == undefined) {