ActionRequestValidationException on deleteIndex() during beforeEach()

Hello --

I'm noticing the following in IndexCrud.scala:
```
trait DeleteIndex {
  self: Indexer =>
  def deleteIndex(indices: Iterable[String] = Nil, timeout: Option[String] = None) = deleteIndex_send(indices, timeout).actionGet
  def deleteIndex_send(indices: Iterable[String] = Nil, timeout: Option[String] = None) = deleteIndex_prepare(indices, timeout).execute
  def deleteIndex_prepare(indices: Iterable[String] = Nil, timeout: Option[String] = None) = {
    val request = client.admin.indices.prepareDelete(indices.toArray: _*)
    timeout foreach { request.setTimeout(_) }
    request
  }

  /** caveat: if none of the indices exists, we will encounter a validation exception */
  def deleteIndexIfExists(indices: Iterable[String] = Nil, timeout: Option[String] = None) = deleteIndexIfExists_send(indices, timeout).actionGet
  def deleteIndexIfExists_send(indices: Iterable[String] = Nil, timeout: Option[String] = None) = deleteIndexIfExists_prepare(indices, timeout).execute
  def deleteIndexIfExists_prepare(indices: Iterable[String] = Nil, timeout: Option[String] = None) = {
    val existing = indices filter (exists(_).isExists)
    val toDelete: Iterable[String] = if (existing.isEmpty) null else existing
    deleteIndex_prepare(toDelete, timeout)
  }
}
```
How are these tests ever passing if they throw an exception on delete() when I'm starting from scratch with no indexes? Are you doing some special prep step that I'm not catching?

Here's the exception:
```
org.elasticsearch.action.ActionRequestValidationException: Validation Failed: 1: index / indices is missing;
```

Thank you,

Martin