NullPointerException in PropertiesResponder.makeJson() when page has empty <Suites> property

[dsporov]

Describe the bug
Requesting ?properties&format=json for a page that has an empty <Suites/> element in its properties.xml causes a NullPointerException on the server. The HTML ?properties endpoint is unaffected.

To Reproduce
Steps to reproduce the behavior:

1. Replace properties.xml for any FitNesse page with the properties.xml from the attachment.
2. Request http://localhost:8081/<PageName>?properties&format=json.

Expected behavior
A valid JSON response is returned with an empty or absent Suites field.

Screenshots

Sample Wiki Structure/content
properties.zip

Stack Trace
v20251025
java.lang.NullPointerException
at fitnesse.responders.editing.PropertiesResponder.makeJson(PropertiesResponder.java:112)
at fitnesse.responders.editing.PropertiesResponder.makeContent(PropertiesResponder.java:88)
at fitnesse.responders.editing.PropertiesResponder.makeResponse(PropertiesResponder.java:81)
at fitnesse.FitNesseExpediter.createGoodResponse(FitNesseExpediter.java:143)
at fitnesse.FitNesseExpediter.makeResponse(FitNesseExpediter.java:110)
at fitnesse.FitNesseExpediter.run(FitNesseExpediter.java:52)
at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at java.base/java.lang.Thread.run(Thread.java:829)

Configuration:

• OS: Windows Server 2022
• Browser edge
• Versions v20200501 and v20251025 of FitNesse
• Test System: Slim
• Plugins in use: -

Additional context
The empty was likely written by an older version of FitNesse.