Use field Null to assign to a MySqlGuid in order to represent a Null value. In this case a guid inserted in a field of a table will be Null.
Requirements
Target Platforms: 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