Allow aggregate method with opt

[amz]

            MongoQueryParser parser = new MongoQueryParser();
            MongoQuery mongoQuery = parser.parse(longQuery, new HashMap());
            BasicDBList dbObjList = mongoQuery.execute(db);

Query is an aggregation: db.events.aggregate([....])

I have an exception: Caused by: com.mongodb.MongoCommandException: Command failed with error 16945: 'Exceeded memory limit for $group, but didn't allow external sort. Pass allowDiskUse:true to opt in.

When i try to pass it like: db.events.aggregate([....],{ allowDiskUse: true }) then i have an exception:
java.lang.RuntimeException: invalid query
at com.ee.dynamicmongoquery.MongoQueryParser.parse(MongoQueryParser.scala:31)
at com.ee.dynamicmongoquery.MongoQueryParser.parse(MongoQueryParser.scala:27)
......
Caused by: java.lang.ClassCastException: null

How can i pass allowDiskUse:true to query?

[amz]

I have created pull request to fix this #7