Unexplained 500 errors in our development server

When running the development server for this project, resources like /favicon.ico are triggering 500s rather than 404s. Here is a stack trace which is being logged which indicates the 'cause' of the 500. As you can see, it's not within our server code and somehow related to resources.

2020-11-25 14:39:11.822:WARN:oejs.HttpChannel:qtp505036866-44: /favicon.ico
java.lang.NullPointerException: Response map is nil
	at ring.util.servlet$update_servlet_response.invokeStatic(servlet.clj:100)
	at ring.util.servlet$update_servlet_response.invoke(servlet.clj:91)
	at ring.util.servlet$update_servlet_response.invokeStatic(servlet.clj:95)
	at ring.util.servlet$update_servlet_response.invoke(servlet.clj:91)
	at ring.adapter.jetty$proxy_handler$fn__13225.invoke(jetty.clj:26)
	at ring.adapter.jetty.proxy$org.eclipse.jetty.server.handler.AbstractHandler$ff19274a.handle(Unknown Source)
	at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:97)
	at org.eclipse.jetty.server.Server.handle(Server.java:499)
	at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:311)
	at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:258)
	at org.eclipse.jetty.io.AbstractConnection$2.run(AbstractConnection.java:544)
	at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:635)
	at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:555)
	at java.lang.Thread.run(Thread.java:748)

This create a lot of noise in the development server, which is not ideal! Missing resources should be handled as 404s, not 500s.

Follow the instructions here to get the server started. You do not need to log in to reproduce this.