def empty_value(attribute)
      type = java_type(attribute) || return
      if type.primitive? then
        type.name == 'boolean' ? false : 0
      else
        self.class.empty_value(attribute)
      end
    end
def empty_value(attribute)
      type = java_type(attribute) || return
      if type.primitive? then
        type.name == 'boolean' ? false : 0
      else
        self.class.empty_value(attribute)
      end
    end
Returns 0 if attribute is a Java primitive number,
 +false+ if attribute is a Java primitive boolean,
 an empty collectin if the Java attribute is a collection,
 nil otherwise.