'Declaration Public Property AllowNull As Infragistics.Win.DefaultableBoolean
public Infragistics.Win.DefaultableBoolean AllowNull {get; set;}
When AllowNull is True, the control will allow the user to clear out the text of the control and interpret this as a null value. The null value will be considered acceptable for the purposes of validation. IsItemInList will return true for a value of null or DBNull, even if no such item exists on the list. LimitToList will permit the control to lose focus when the value is null, even when no null item exists on the list. The control will display the as empty; it will not attempt to look for a null item on the list in order to determine the display text.
When this property is Default, the control will have the same behavior as when the property is False.
Target Platforms: Windows 10, Windows 8.1, Windows 8, Windows 7, Windows Server 2012, Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2