Failed to build a shell project when 'distributed builds' is enabled

Steps:

• Unpack continuum 1.3.5 binaries, start the continuum instance, create an account then login.
• Enable distributed builds here http://localhost:8080/continuum/admin/configuration!input.action
• Add and enable a new build agent here http://localhost:8080/continuum/security/buildAgentList.action
• Go to the build management menu and add a project group
• Add a new shell project with a subversion scm
• Edit the build definition, make sure that the values are correct, then save the configuration.
  e.g.
  shell executable: start_selenium_tests.sh
  type: shell
  see attached screenshot for the build definition.
• Build the project

Actual Result:
The project did not build successfully.

The following error was returned:

java.lang.Exception: Failed to build projects.
at org.apache.continuum.distributed.transport.slave.SlaveBuildAgentTransportClient.buildProjects(SlaveBuildAgentTransportClient.java:100)
at org.apache.continuum.builder.distributed.executor.DistributedBuildProjectTaskExecutor.executeTask(DistributedBuildProjectTaskExecutor.java:130)
at org.apache.continuum.builder.distributed.executor.ThreadedDistributedBuildTaskQueueExecutor$ExecutorRunnable$1.run(ThreadedDistributedBuildTaskQueueExecutor.java:134)
at edu.emory.mathcs.backport.java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:442)
at edu.emory.mathcs.backport.java.util.concurrent.FutureTask.run(FutureTask.java:176)
at edu.emory.mathcs.backport.java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:987)
at edu.emory.mathcs.backport.java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:528)
at java.lang.Thread.run(Thread.java:595)
Caused by: java.lang.RuntimeException: Could not execute RPC method buildProjects
at com.atlassian.xmlrpc.RPCCallMethodInterceptor.invoke(RPCCallMethodInterceptor.java:67)
at $Proxy17.buildProjects(Unknown Source)
at org.apache.continuum.distributed.transport.slave.SlaveBuildAgentTransportClient.buildProjects(SlaveBuildAgentTransportClient.java:94)
... 7 more
Caused by: org.apache.xmlrpc.common.XmlRpcExtensionException: Null values aren't supported, if isEnabledForExtensions() == false
at org.apache.xmlrpc.common.TypeFactoryImpl.getSerializer(TypeFactoryImpl.java:115)
at com.atlassian.xmlrpc.BinderTypeFactory.getSerializer(BinderTypeFactory.java:64)
at org.apache.xmlrpc.serializer.MapSerializer.writeValue(MapSerializer.java:70)
at org.apache.xmlrpc.serializer.MapSerializer.writeEntry(MapSerializer.java:64)
at org.apache.xmlrpc.serializer.MapSerializer.writeData(MapSerializer.java:81)
at org.apache.xmlrpc.serializer.MapSerializer.write(MapSerializer.java:88)
at org.apache.xmlrpc.serializer.ObjectArraySerializer.writeObject(ObjectArraySerializer.java:50)
at org.apache.xmlrpc.serializer.ObjectArraySerializer.writeData(ObjectArraySerializer.java:55)
at org.apache.xmlrpc.serializer.ObjectArraySerializer.write(ObjectArraySerializer.java:62)
at org.apache.xmlrpc.serializer.XmlRpcWriter.writeValue(XmlRpcWriter.java:172)
at org.apache.xmlrpc.serializer.XmlRpcWriter.write(XmlRpcWriter.java:77)
at org.apache.xmlrpc.client.XmlRpcStreamTransport$ReqWriterImpl.write(XmlRpcStreamTransport.java:67)
at org.apache.xmlrpc.client.XmlRpcHttpTransport$ByteArrayReqWriter.<init>(XmlRpcHttpTransport.java:23)
at org.apache.xmlrpc.client.XmlRpcHttpTransport.newReqWriter(XmlRpcHttpTransport.java:106)
at org.apache.xmlrpc.client.XmlRpcStreamTransport.sendRequest(XmlRpcStreamTransport.java:139)
at org.apache.xmlrpc.client.XmlRpcHttpTransport.sendRequest(XmlRpcHttpTransport.java:94)
at org.apache.xmlrpc.client.XmlRpcSunHttpTransport.sendRequest(XmlRpcSunHttpTransport.java:44)
at org.apache.xmlrpc.client.XmlRpcClientWorker.execute(XmlRpcClientWorker.java:53)
at org.apache.xmlrpc.client.XmlRpcClient.execute(XmlRpcClient.java:166)
at org.apache.xmlrpc.client.XmlRpcClient.execute(XmlRpcClient.java:157)
at org.apache.xmlrpc.client.XmlRpcClient.execute(XmlRpcClient.java:146)
at com.atlassian.xmlrpc.RPCCallMethodInterceptor.invoke(RPCCallMethodInterceptor.java:62)
... 9 more