Unless in edit mask mode or in date-time editing withDateTimeInput set to True, the user can enter a null value in one of the following ways:
If the user enters a null value (either by entering an empty string or NullText, see above), input string validation and parsing are skipped, see Input string validation (PreValidation) and Parsing (Updating) Data. However, PostValidation is performed in this case as in all others, see Typed value validation (PostValidation).