UnsupportedOperationException thrown when sending message from client to Number

[ammendonca]

Is this a BUG REPORT or FEATURE REQUEST?:
/kind bug

What happened:

When sending a message from a client to a number [associated with an application], using Olympus, the message is properly sent and the application executed and response received but an exception is thrown in the console:

...
23:54:37,250 INFO  [org.restcomm.connect.telephony.api.util.B2BUAHelper] (RestComm-akka.actor.default-dispatcher-107) SIP SESSION is NULL
23:54:37,251 INFO  [org.mobicents.servlet.sip.core.session.SipSessionImpl] (MSS-Executor-Thread-6) Invalidating the sip session (43877593_367736b8_57a5b08a_3f4736ef;[email protected];3f4736ef;RestComm)
23:54:37,251 INFO  [org.restcomm.connect.sms.SmsService] (RestComm-akka.actor.default-dispatcher-107) Is SipApplicationSession valid: true
23:54:37,251 INFO  [org.mobicents.servlet.sip.core.session.SipApplicationSessionImpl] (MSS-Executor-Thread-6) Invalidating the following sip application session 3f4736ef;RestComm
23:54:37,252 INFO  [org.mobicents.servlet.sip.core.session.SipApplicationSessionImpl] (MSS-Executor-Thread-6) The following sip application session 3f4736ef;RestComm has been invalidated
23:54:37,251 ERROR [org.restcomm.connect.commons.faulttolerance.RestcommSupervisorStrategy] (RestComm-akka.actor.default-dispatcher-108) RestcommSupervisorStrategy, actor exception handling. Actor path akka://RestComm/user/$c/$f, exception cause java.lang.UnsupportedOperationException, default exception handling strategy Resume
23:54:37,251 ERROR [org.restcomm.connect.sms.SmsSession] (RestComm-akka.actor.default-dispatcher-107) null: java.lang.UnsupportedOperationException
	at com.google.common.collect.ImmutableMap.put(ImmutableMap.java:318) [guava-14.0.1.jar:]
	at org.restcomm.connect.sms.SmsSession.response(SmsSession.java:271) [restcomm-connect.sms-8.3.1-193.jar:8.3.1-193]
	at org.restcomm.connect.sms.SmsSession.onReceive(SmsSession.java:246) [restcomm-connect.sms-8.3.1-193.jar:8.3.1-193]
	at akka.actor.UntypedActor$$anonfun$receive$1.applyOrElse(UntypedActor.scala:159) [akka-actor_2.10-2.1.2.jar:]
	at akka.actor.ActorCell.receiveMessage(ActorCell.scala:425) [akka-actor_2.10-2.1.2.jar:]
	at akka.actor.ActorCell.invoke(ActorCell.scala:386) [akka-actor_2.10-2.1.2.jar:]
	at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:230) [akka-actor_2.10-2.1.2.jar:]
	at akka.dispatch.Mailbox.run(Mailbox.scala:212) [akka-actor_2.10-2.1.2.jar:]
	at akka.dispatch.ForkJoinExecutorConfigurator$MailboxExecutionTask.exec(AbstractDispatcher.scala:506) [akka-actor_2.10-2.1.2.jar:]
	at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:262) [scala-library-2.10.1.jar:]
	at scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:975) [scala-library-2.10.1.jar:]
	at scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1478) [scala-library-2.10.1.jar:]
	at scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:104) [scala-library-2.10.1.jar:]

What you expected to happen:
Expected an exception-free log :)

How to reproduce it (as minimally and precisely as possible):
Start restcomm, sign in to Olympus with any client, send a message to a number and the exception should show.

Anything else we need to know?:
—

Environment:

• Restcomm Connect version (from startup logs): 8.3.1
• Cloud provider or hardware configuration: N/A
• OS (e.g. from /etc/os-release): macOS 10.13.3
• Kernel (e.g. uname -a): Darwin Kernel Version 17.4.0
• Deployment method (e.g. docker-compose, with linked docker-compose.yml file,
  or application server info + deployment option): ./start-restcomm.sh
• Others: N/A