This is the same question as: Explicit Element Closing Tags with System.Xml.Linq Namespace

but I use Net 4.0 and the answers do not work anymore.

The problem is I save tags with no values really, and my output XML looks like this:

<field/>

But what I need is always opening and closing tag, i.e.

<field></field>

QUESTION: how to do it?

Edits

1

Adding empty nodes:

if (field_xml == null) // always true, because I create the file for the first time
{
    field_xml = new XElement(XMLKeys.field,String.Empty);
    table_xml.Add(field_xml);
}
field_xml.SetAttributeValue(XMLKeys.name, field_info.Name);
// ... setting some other attributes of this node

and later, saving the xml:

var writer = new FullEndingXmlTextWriter(parameters.OutputFilename, Encoding.UTF8);
root_xml.Save(writer);

FullEndingXmlTextWriter is the specialized class which The Evil Greebo pointed out (it is supposed to force explicit closing tag).