MessageStreamImpl#merge shouldn't assume that the input collection is mutable

Exception in thread "main" org.apache.samza.SamzaException: Failed to run application
    at org.apache.samza.runtime.RemoteApplicationRunner.run(RemoteApplicationRunner.java:64)
    at org.apache.samza.runtime.ApplicationRunnerMain.main(ApplicationRunnerMain.java:67)
Caused by: java.lang.UnsupportedOperationException
    at java.util.AbstractList.add(AbstractList.java:148)
    at java.util.AbstractList.add(AbstractList.java:108)
    at org.apache.samza.operators.MessageStreamImpl.merge(MessageStreamImpl.java:189)
    at samza.examples.wikipedia.application.WikipediaApplication.init(WikipediaApplication.java:39)
    at org.apache.samza.runtime.AbstractApplicationRunner.getExecutionPlan(AbstractApplicationRunner.java:100)
    at org.apache.samza.runtime.RemoteApplicationRunner.run(RemoteApplicationRunner.java:52)