addExposedPort fails when called after withExposedPorts #451

In my use case I configure a container using withExposedPorts method and then process this container in common code by exposing one more port. I would like to call addExposedPort, but this fails with exception:

java.lang.UnsupportedOperationException
	at java.util.AbstractList.add(AbstractList.java:148)
	at java.util.AbstractList.add(AbstractList.java:108)
	at org.testcontainers.containers.GenericContainer.addExposedPort(GenericContainer.java:532)

So I have to first get all exposed ports, add new one and call withExposedPorts again.

If the code in withExposedPorts would be changed from

this.setExposedPorts(asList(ports));

to

this.setExposedPorts(new ArrayList(asList(ports)));

or to

this.setExposedPorts(Lists.newArrayList(ports));

this would solve the problem.