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System.DBNull (class)

System.DBNull represents a non-existing value.
The concept of non-existing values is most probably borrowed from SQL's special null value/data type.
DBNull is a singleton.
DBNull and null are not the same thing.

Equivalence to System.Convert.DBNull

System.DBNull is equivalent to System.Convert.DBNull, as can be demonstrated with the following PowerShell statement: 
[System.Convert]::DBNull.Equals([System.DBNull]::Value)

See also

The IsDBNull method of the Microsoft.VisualBasic.Information class.
Compare with the VBA null value.

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