I've identified another regression between Lift 2.0/2.1-M1 and Lift 2.1-RC1/RC2.

Given the following code:

import net.liftweb.common._
import net.liftweb.mongodb.record._
import net.liftweb.record.field._

class SimpleUser extends MongoRecord[SimpleUser] with MongoId[SimpleUser] {
  override def meta = SimpleUser

  object name extends StringField(this, 50) {
    setBox(Empty)
    override def optional_? = true
  }
}

object SimpleUser extends SimpleUser with MongoMetaRecord[SimpleUser] {
  override def createRecord = new SimpleUser // This line needs to be commented out to compile under Lift 2.1-RC1/2
}

Under Lift 2.0 and Lift 2.1-M1, you get the following (expected) behavior:

scala> SimpleUser.createRecord.asDBObject
res0: com.mongodb.DBObject = { "_id" : { "$oid" : "4c93df29cd1395091868b217"}}

The "name" field is optional_?=true and has been set to be Empty, so it is excluded from the DBObject.

Under Lift 2.1-RC1 and Lift 2.1-RC2, you get the following (unexpected) behavior:

scala> SimpleUser.createRecord.asDBObject
res0: com.mongodb.DBObject = { "name" : "" , "_id" : { "$oid" : "4c93dd3f09b0950958646c6e"}}

The "name" field is still optional_?=true and set to Empty, but now the DBObject includes the "name" field with an empty string (the default value).

I suspect this has to do with the toValueType/toBoxMyType roundtrip in TypedField, but I'm not sure and I do not have a fix yet.