For our use case, we add ~186 facts to the report. Sometimes the value is null, and the receiving party does not allow empty facts. So instead of adding 102 if-statements surrounding the AddFact methods we just cleanup the report afterwards.

We cannot just loop all facts and remove where Value is null, because the Remove method on the FactCollection will fail with a NullReferenceException. Because the base type collection relies on the GetHashCode and Equals methods of the Fact class, which both assume Value is never null.

https://github.com/dgm9704/Xoxo/blob/main/Diwen.Xbrl/Xml/Fact.cs#L207
https://github.com/dgm9704/Xoxo/blob/main/Diwen.Xbrl/Xml/Fact.cs#L215

Our solution is now to remove by index, but I felt like fixing this underlying issue would be the better approach:

        for (int i = report.Facts.Count - 1; i >= 0; i--)
        {
            if (string.IsNullOrEmpty(report.Facts[i].Value))
            {
                report.Facts.RemoveAt(i); // cannot use Remove(fact) here because of `NullReferenceException`
            }
        }