DBObject ref = new BasicDBObject();
ref.put("myfield", Pattern.compile(".myValue." , Pattern.CASE_INSENSITIVE));
DBCursor cur = coll.find(ref);

produces the following exception:

java.lang.RuntimeException: db error [EOO Before end of object]
at com.mongodb.DBApiLayer$MyCollection.find(DBApiLayer.java:324)
at com.mongodb.DBCursor._check(DBCursor.java:237)
at com.mongodb.DBCursor._hasNext(DBCursor.java:367)
at com.mongodb.DBCursor.hasNext(DBCursor.java:392)
...

when leaving out the case insensitive parameter on pattern construction the query works fine.