An exception caught during sampling

[artourkin]

A exception is caught when calculating samples using Selective Feature Distribution algorithm.
The message is the following:

Caused by: com.mongodb.CommandResult$CommandFailure: command failed [command failed [mapreduce] { "serverUsed" : "128.130.204.29:27017" , "ok" : 0.0 , "errmsg" : "MR parallel processing failed: { errmsg: "exception: _id cannot be an array", code: 10099, ok: 0.0 }"}