gorm - Grails, querying self-referencing table -

i have table self-referencing field:

class book{      integer id     string name     book version } 

when add books without "version", version field null have query book table records don't have version (their version field null), following code won't work:

def results = book.withcriteria{     eq("version", "null") }  

but i'm getting exception:

org.hibernate.propertyaccessexception: illegalargumentexception occurred calling getter of book.id 

what query should use?

version keyword in gorm used optimistic locking. modify domain , criteria below make criteria return appropriate results.

//domain

class book {     integer id     string name     book bookversion } 

//criteria

def book = new book(name: "test", version: null) book.id = 1 book.save(flush: true)  def results = book.withcriteria{     isnull("bookversion") }  assert results && results[0] instanceof book 

also note, bookversion in question of type book, cannot compared string null.