A string specifying the name of the column in the data source or a null reference (Nothing in Visual Basic) if the SourceOrdinal
The SourceColumn and SourceOrdinal properties are mutually exclusive. The most recently set value takes priority.
Setting the SourceColumn property causes the SourceOrdinal property to be set to -1. Setting the SourceOrdinal property causes
the SourceColumn property to be set to a null reference (Nothing in Visual Basic).
It is an error to set SourceColumn to null or the empty string.