fix(binding-mqtt): replace ?? with || for mqv:filter and mqv:topic fallback

The nullish coalescing operator (??) only triggers on null or undefined,
not on empty strings. When the URL path is '/', pathname.slice(1) returns
'' which is falsy but not null/undefined, causing mqv:filter and mqv:topic
to be silently ignored.

Fixes #1508

Author: jona42-ui

packages/binding-mqtt/src/mqtt-client.ts

@@ -65,7 +65,7 @@ export default class MqttClient implements ProtocolClient {
         const brokerUri: string = `${this.scheme}://` + requestUri.host;
         // Keeping the path as the topic for compatibility reasons.
         // Current specification allows only form["mqv:filter"]
-        const filter = requestUri.pathname.slice(1) ?? form["mqv:filter"];
+        const filter = requestUri.pathname.slice(1) || form["mqv:filter"];
 
         let pool = this.pools.get(brokerUri);
 
@@ -95,7 +95,7 @@ export default class MqttClient implements ProtocolClient {
         const brokerUri: string = `${this.scheme}://` + requestUri.host;
         // Keeping the path as the topic for compatibility reasons.
         // Current specification allows only form["mqv:filter"]
-        const filter = requestUri.pathname.slice(1) ?? form["mqv:filter"];
+        const filter = requestUri.pathname.slice(1) || form["mqv:filter"];
 
         let pool = this.pools.get(brokerUri);
 
@@ -125,7 +125,7 @@ export default class MqttClient implements ProtocolClient {
     public async writeResource(form: MqttForm, content: Content): Promise<void> {
         const requestUri = new url.URL(form.href);
         const brokerUri = `${this.scheme}://${requestUri.host}`;
-        const topic = requestUri.pathname.slice(1) ?? form["mqv:topic"];
+        const topic = requestUri.pathname.slice(1) || form["mqv:topic"];
 
         let pool = this.pools.get(brokerUri);