How do I include records into XML element C#

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C#

Hi...I would like to please you guys to help me creating this xml file...I've tried with this code above but I've got some Errors...even when I declarate docRecords outside of For loop it gives me an Error:

An unhandled exception of type 'System.NullReferenceException' occurred in XMLGenUsingLINQ.exe

Additional information: The object reference not defined as Object Instance...something like that...I've translated from my language :)

Here is the Schema I want to get:

<Report> 
	<Versao>1</Versao> 
	<Details> 
		<Record> 
			<ID>1</ID> 
			<Reference>20171</Reference> 
		</Record> 
		<Record> 
			<ID>2</ID> 
			<Reference>20172</Reference> 
		</Record> 
	</Details> 
</Report>

What I have tried:

I've tried this:

XDocument docHeader = new XDocument(
    new XElement("Report",
    new XElement("Versao", "1"),
    new XElement("Details", "")
));

for (int i = 0; i < 2; i++)
{
    var docRecords = new XElement("Record",
                    new XElement("ID", i.ToString()),
                    new XElement("Reference", "2017" + i.ToString())
        );
}

docHeader.Element("Details").Add(docRecords);
using (var writer = new XmlTextWriter("C:\\Reports\\MyReport.xml", new UTF8Encoding(false)))
{
    docHeader.Save(writer);
}