An exception of type 'System.InvalidCastException' occurred in factory.dll but was not handled in user code

Hi,
I have a function below which throw the error from  (Throw ex). error message is "
An exception of type 'System.InvalidCastException' occurred in factory.dll but was not handled in user code
Additional information: Conversion from type 'DBNull' to type 'String' is not valid.".
shall I handle this error or not? if yes, How?Thanks.

Public Shared Sub ThrowException(ByVal ex As Exception, ByVal EventType As EventLogEntryType)             LogException(ex, EventType)             Throw ex         End Sub