Fix for #8

Author: yGuy

package.json

@@ -1,6 +1,6 @@
 {
   "name": "chatgpt-mattermost-bot",
-  "version": "1.3.0",
+  "version": "1.3.1",
   "private": true,
   "scripts": {
     "start": "node ./src/botservice.js"

src/process-graph-response.js

@@ -4,7 +4,7 @@ const { Log } = require('debug-level')
 const log = new Log('bot')
 
 const yFilesGPTServerUrl = process.env['YFILES_SERVER_URL']
-const yFilesEndpoint = new URL('/json-to-svg', yFilesGPTServerUrl)
+const yFilesEndpoint = yFilesGPTServerUrl ? new URL('/json-to-svg', yFilesGPTServerUrl) : undefined
 
 /**\
  * @param {string} content