Failed to execute phase [fetch], [reduce]

Hi there,

On graylog 1.2 I have recently been getting the following message on a Quick Values chart for a field called "response_code" (its HTTP response values).
It seems to happen periodically, with it sometimes returning data sometimes not.

The web frontend returns a 400, with a Bad Request response and no other information.

This is from the logs on the graylog server:

```
2015-12-10T17:03:44.193Z WARN [SearchResource] Unable to execute search: Failed to execute phase [fetch], [reduce]
2015-12-10T17:03:54.229Z ERROR [AnyExceptionClassMapper] Unhandled exception in REST resource
org.elasticsearch.action.search.ReduceSearchPhaseException: Failed to execute phase [fetch], [reduce]
at org.elasticsearch.action.search.type.TransportSearchQueryThenFetchAction$AsyncAction$2.onFailure(TransportSearchQueryThenFetchAction.java:159)
at org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:41)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.ClassCastException: org.elasticsearch.search.aggregations.bucket.terms.LongTerms$Bucket cannot be cast to org.elasticsearch.search.aggregations.bucket.terms.StringTerms$Bucket
at org.elasticsearch.search.aggregations.bucket.terms.StringTerms$Bucket.compareTerm(StringTerms.java:85)
at org.elasticsearch.search.aggregations.bucket.terms.InternalOrder$4.compare(InternalOrder.java:87)
at org.elasticsearch.search.aggregations.bucket.terms.InternalOrder$4.compare(InternalOrder.java:83)
at org.elasticsearch.search.aggregations.bucket.terms.InternalOrder$CompoundOrder$CompoundOrderComparator.compare(InternalOrder.java:284)
at org.elasticsearch.search.aggregations.bucket.terms.InternalOrder$CompoundOrder$CompoundOrderComparator.compare(InternalOrder.java:270)
at org.elasticsearch.search.aggregations.bucket.terms.support.BucketPriorityQueue.lessThan(BucketPriorityQueue.java:37)
at org.elasticsearch.search.aggregations.bucket.terms.support.BucketPriorityQueue.lessThan(BucketPriorityQueue.java:26)
at org.apache.lucene.util.PriorityQueue.upHeap(PriorityQueue.java:225)
at org.apache.lucene.util.PriorityQueue.add(PriorityQueue.java:133)
at org.apache.lucene.util.PriorityQueue.insertWithOverflow(PriorityQueue.java:149)
at org.elasticsearch.search.aggregations.bucket.terms.InternalTerms.reduce(InternalTerms.java:195)
at org.elasticsearch.search.aggregations.InternalAggregations.reduce(InternalAggregations.java:140)
at org.elasticsearch.search.aggregations.bucket.InternalSingleBucketAggregation.reduce(InternalSingleBucketAggregation.java:79)
at org.elasticsearch.search.aggregations.InternalAggregations.reduce(InternalAggregations.java:140)
at org.elasticsearch.search.controller.SearchPhaseController.merge(SearchPhaseController.java:407)
at org.elasticsearch.action.search.type.TransportSearchQueryThenFetchAction$AsyncAction$2.doRun(TransportSearchQueryThenFetchAction.java:147)
at org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:36)
... 3 more
2015-12-10T17:03:59.289Z ERROR [AnyExceptionClassMapper] Unhandled exception in REST resource
org.elasticsearch.action.search.ReduceSearchPhaseException: Failed to execute phase [fetch], [reduce]
at org.elasticsearch.action.search.type.TransportSearchQueryThenFetchAction$AsyncAction$2.onFailure(TransportSearchQueryThenFetchAction.java:159)
at org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:41)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.ClassCastException: org.elasticsearch.search.aggregations.bucket.terms.LongTerms$Bucket cannot be cast to org.elasticsearch.search.aggregations.bucket.terms.StringTerms$Bucket
at org.elasticsearch.search.aggregations.bucket.terms.StringTerms$Bucket.compareTerm(StringTerms.java:85)
at org.elasticsearch.search.aggregations.bucket.terms.InternalOrder$4.compare(InternalOrder.java:87)
at org.elasticsearch.search.aggregations.bucket.terms.InternalOrder$4.compare(InternalOrder.java:83)
at org.elasticsearch.search.aggregations.bucket.terms.InternalOrder$CompoundOrder$CompoundOrderComparator.compare(InternalOrder.java:284)
at org.elasticsearch.search.aggregations.bucket.terms.InternalOrder$CompoundOrder$CompoundOrderComparator.compare(InternalOrder.java:270)
at org.elasticsearch.search.aggregations.bucket.terms.support.BucketPriorityQueue.lessThan(BucketPriorityQueue.java:37)
at org.elasticsearch.search.aggregations.bucket.terms.support.BucketPriorityQueue.lessThan(BucketPriorityQueue.java:26)
at org.apache.lucene.util.PriorityQueue.upHeap(PriorityQueue.java:225)
at org.apache.lucene.util.PriorityQueue.add(PriorityQueue.java:133)
at org.apache.lucene.util.PriorityQueue.insertWithOverflow(PriorityQueue.java:149)
at org.elasticsearch.search.aggregations.bucket.terms.InternalTerms.reduce(InternalTerms.java:195)
at org.elasticsearch.search.aggregations.InternalAggregations.reduce(InternalAggregations.java:140)
at org.elasticsearch.search.aggregations.bucket.InternalSingleBucketAggregation.reduce(InternalSingleBucketAggregation.java:79)
at org.elasticsearch.search.aggregations.InternalAggregations.reduce(InternalAggregations.java:140)
at org.elasticsearch.search.controller.SearchPhaseController.merge(SearchPhaseController.java:407)
at org.elasticsearch.action.search.type.TransportSearchQueryThenFetchAction$AsyncAction$2.doRun(TransportSearchQueryThenFetchAction.java:147)
at org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:36)
... 3 more

```