Resize of hostgroup failing with NPE

[duncangrant]

When extending cluster to size 2 - we get:

Failed after 26ms: NullPointerException

java.lang.NullPointerException
at com.google.common.base.Preconditions.checkNotNull(Preconditions.java:210)
at com.google.common.base.Joiner.toString(Joiner.java:433)
at com.google.common.base.Joiner.appendTo(Joiner.java:108)
at com.google.common.base.Joiner.appendTo(Joiner.java:152)
at com.google.common.base.Joiner.join(Joiner.java:193)
at com.google.common.base.Joiner.join(Joiner.java:183)
at com.google.common.base.Joiner.join(Joiner.java:201)
at org.apache.brooklyn.util.ssh.BashCommands.appendToEtcHosts(BashCommands.java:734)
at io.brooklyn.ambari.agent.AmbariAgentSshDriver.install(AmbariAgentSshDriver.java:99)
at org.apache.brooklyn.entity.software.base.AbstractSoftwareProcessDriver$2$6.run(AbstractSoftwareProcessDriver.java:165)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at org.apache.brooklyn.util.core.task.DynamicSequentialTask$DstJob.call(DynamicSequentialTask.java:364)
at org.apache.brooklyn.util.core.task.BasicExecutionManager$SubmissionCallable.call(BasicExecutionManager.java:565)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)