What is the correct syntax to pass a null value for a timestamp column using Npgsql? - amazon-redshift

Question

I have an AWS Redshift table with a timestamp type column.
create table if not exists testtimestampfields
(
testid varchar(50) not null,
creationdate timestamp null
);
Since the creationdate field permits null, I thought I could pass a null DateTime as the parameter value when inserting records.
[Fact]
public async Task Can_insert_null_timestamp_field()
{
// Custom class that calls GetClusterCredentials and returns a connection with the user and password...
await using var conn = await _redshiftConnectionManager.GetConnectionAsync();
await conn.OpenAsync();
await using var cmd = new NpgsqlCommand(
#"insert into testtimestampfields(testid, creationdate) values (#testid, #creationdate);", conn);
var testidParam = cmd.Parameters.Add("#testid", NpgsqlDbType.Varchar);
var creationDateParam = cmd.Parameters.Add("#creationdate", NpgsqlDbType.Timestamp);
testidParam.Value = Guid.NewGuid().ToString();
creationDateParam.Value = null;
await cmd.ExecuteNonQueryAsync();
}
But when I try this await cmd.ExecuteNonQueryAsync(); fails with:
System.InvalidCastException: Parameter #creationdate must be set
System.InvalidCastException
Parameter #creationdate must be set
at Npgsql.NpgsqlParameter.ValidateAndGetLength()
at Npgsql.NpgsqlParameterCollection.ValidateAndBind(ConnectorTypeMapper typeMapper)
at Npgsql.NpgsqlCommand.ExecuteReader(CommandBehavior behavior, Boolean async, CancellationToken cancellationToken)
at Npgsql.NpgsqlCommand.ExecuteReader(CommandBehavior behavior, Boolean async, CancellationToken cancellationToken)
at Npgsql.NpgsqlCommand.ExecuteNonQuery(Boolean async, CancellationToken cancellationToken)
...
What is the correct syntax to pass a null value for a timestamp column using Npgsql?

Answer 1

Changing null to DBNull.Value works.
creationDateParam.Value = DBNull.Value;
Using a .NET DateTime? variable to set the parameter value conditionally:
creationDateParam.Value = dateTime.HasValue ? dateTime.Value : DBNull.Value;