.Net C# String.Join how to output "null" instead of empty string if element value is null?

Question

According to the MSDN docs for String.Join "If any element in value is null, an empty string is used instead."

The code I have pulls data out of a DataTable

rotationValues = string.Join<object>(", ",
    from r in rotationData.Rows.OfType<DataRow>() select r[5]);

This would result in output similar to this:

8, 7, , 12, , , 13, 

Is there any way to simply have it put "null" in place of an empty string like so:

8, 7, null, 12, null, null, 13, null

Answer 1

You can select

r[5] ?? "null"

instead of just r[5].

Also, just remove the <object> part when you call the generic method. It will still be an IEnumerable<object> that you join, but the compiler will infer the type parameter automatically.

ADDITION after comment:

Your r[5] might be DBNull.Value. Then, this is not a "real" null reference, but its ToString implementation returns "". So in that case, the string.Join documentation wasn't strictly relevant. Therefore, try to select something like

(r[5] == null || DBNull.Value.Equals(r[5])) ? "null" : r[5]

or maybe

(r[5] == null || r[5] is DBNull) ? "null" : r[5]

Hope it helps.