Unless in edit mask mode or in date-time editing with DateTimeInput set to True, the user can enter a null value in one of the following ways:

• If the control text equals NullText, the resulting value is null. The effective NullText value here is determined by NullText. Comparison with NullText is case-sensitive or not depending on the CaseSensitive property.
• Clearing the control, entering an empty string results in null value if the C1TextBox.EmptyAsNull property is set to True (it is False by default).
• In programmatic parsing, DBNull value can be returned by the programmer in the Parsing event.

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).