Table adapters generate their own interface based on the
methods you create. For instance, if a table that has the fields ID, Name, and
Text, and the adapter generates the insert, update, and delete SQL statements,
the adapter will create overloaded Insert, Update, and Delete methods with these
fields as the parameters. However, you will notice that it will use nullable
type values for the value type parameters.
It may seem that a nullable type will be equivalent to
DBNull, but the table adapter transforms a nullable type to DBNull, when the
final execution is performed. The adapter has its own interface for doing so.
However, when using a table adapter to return a custom data table and rows,
there are special methods for determining if a field is null, and for setting
it to null. These methods are in the construct of Is<ColumnName>Null and
Set<ColumnName>Null. This handles using null values for particular