https://learn.microsoft.com/en-us/dotnet/api/system.data.common.dbdatareader.isdbnull?view=netframework-4.8.1&redirectedfrom=MSDN
DbDataReader.IsDBNull(Int32) Method (System.Data.Common) | Microsoft Learn
When overridden in a derived class, gets a value that indicates whether the column contains nonexistent or missing values.
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