When trading over AS2, this error appears in the TE log:

com.cyclonecommerce.tradingengine.transport.UnableToConnectException: Error connecting to HTTP server URL is null:80, timeout=30s (30,000ms); java.net.UnknownHostException: URL is null
   at com.cyclonecommerce.tradingengine.transport.http.HttpClientBase.connect(HttpClientBase.java:169)
   at com.cyclonecommerce.tradingengine.transport.http.HttpClientBase.connect(HttpClientBase.java:131)
   at com.cyclonecommerce.tradingengine.transport.system.production.producers.HttpProducer.send(HttpProducer.java:151)
   at com.cyclonecommerce.tradingengine.transport.system.production.producers.HttpProducer.produce(HttpProducer.java:52)
   at com.cyclonecommerce.tradingengine.transport.system.production.ProducerTask.produce(ProducerTask.java:247)
   at com.cyclonecommerce.tradingengine.transport.system.production.ProducerTask.execute(ProducerTask.java:130)
   at com.cyclonecommerce.util.task.TaskScheduler$WorkerThread.primRun(TaskScheduler.java:435)
   at com.axway.cluster.extensions.thread.EventedThread.run(EventedThread.java:81)
Caused by: java.net.UnknownHostException: URL is null
   at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:177)
   at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366)
   at java.net.Socket.connect(Socket.java:525)
   at com.cyclonecommerce.tradingengine.transport.http.HttpClientBase.connectDirect(HttpClientBase.java:213)
   at com.cyclonecommerce.tradingengine.transport.http.HttpClientBase.connect(HttpClientBase.java:150)
   ... 7 more

The resolution is to provide the correct URL for the trading partner.