Such query 'curl localhost:9200/_stats' returns an 500 error

Hi,
I have a question regarding statistics which can be shown using such query: 'curl localhost:9200/_stats'
It should return high level aggregation and index level stats for all indices. In my case it returns an error:
{"error":"NullPointerException[null]","status":500}

Worth of mention is that all specific stats are working properly e.g. curl http://localhost:9200/_stats/indices shows proper data.
There is only problem with all statistics.I am using 1.5.1 version.

Thanks,
Rafal

That's very unusual, is there anything in your logs at the time of the request?

Unfortunatelly there is nothing in the log which could lead me to something... I hoped that someone saw such error before.