Set blank values to '' or null in Edit SQL.
Mydb.dbEditAllowZeroLength = "True | False(Def)"
This boolean property is for Editing operations. If your table/fields allows zerolength fields then a blank '' will be used in the SQL (field='') when this property is set to true. Otherwise a 'null' will be used. The default is to use 'null' (field=null). This is one of those tiny option that can break you if you do not have it.