// Try and modify the existing lock.
final BasicDBObject lockDoc
= (BasicDBObject)getDbCollection(pMongo, pSvcOptions).findAndModify(query, new BasicDBObject(LockDef.LOCK_ID.field, 1), null, false, new BasicDBObject(SET, toSet), true, false);
if (lockDoc == null) return null;
if (!lockDoc.containsField(LockDef.LOCK_ID.field)) return null;
final ObjectId returnedLockId = lockDoc.getObjectId(LockDef.LOCK_ID.field);
if (returnedLockId == null) return null;
if (!returnedLockId.equals(lockId)) return null;