Is it possible to express that a result may be null/may not be null depending on a Boolean parameter?

[HugoRoss]

In C#, is it possible to express that a result may be null/may not be null depending on a Boolean parameter, something like the following (not compiling) code?

    [return: NotNullWhen(true, "noRowsThrows")]
    public DataRow? ExecuteToDataRow(SqlCommand command, bool noRowsThrows) {
        DataTable dataTable = ExecuteToDataTable(command);
        DataRowCollection rows = dataTable.Rows;
        switch (rows.Count) {
            case 1:
                return rows[0];
            case < 1:
                if (noRowsThrows) throw new ArgumentException($"The command did not return any rows!");
                return null;
        }
        throw new ArgumentException($"The command returned multiple rows!");
    }

[RikkiGibson]

No. We suggest declaring multiple methods in a scenario like this.

If we introduced an attribute like this, the compiler would still only have a limited ability to track what possible values does a boolean expression have, and we would need to do significant work to improve that beyond simple scenarios like ExecuteToDataRow(command, noRowsThrows: true).

    public DataRow? ExecuteToDataRow(SqlCommand command) {
        DataTable dataTable = ExecuteToDataTable(command);
        DataRowCollection rows = dataTable.Rows;
        switch (rows.Count) {
            case 1:
                return rows[0];
            case < 1:
                return null;
        }
        throw new ArgumentException($"The command returned multiple rows!");
    }


    public DataRow ExecuteToRequiredDataRow(SqlCommand command) {
        return ExecuteToDataRow(command) ?? throw new ArgumentException($"The command did not return any rows!");
    }