Unable to remove empty xmlns attribute from XElement using c#

Image This is you xml file

<Root xmlns="http://my.namespace">
    <Firstelement xmlns="">
        <RestOfTheDocument />
    </Firstelement>
</Root>

This is you expect

<Root xmlns="http://my.namespace">
    <Firstelement>
        <RestOfTheDocument />
    </Firstelement>
</Root>

I think the code below is what you want. You need to put each element into the right namespace, and remove any xmlns='' attributes for the affected elements. The latter part is required as otherwise LINQ to XML basically tries to leave you with an element of

<!-- This would be invalid -->
<Firstelement xmlns="" xmlns="http://my.namespace">

Here's the code:

using System;
using System.Xml.Linq;

class Test
{
    static void Main()
    {
        XDocument doc = XDocument.Load("test.xml");
        foreach (var node in doc.Root.Descendants())
        {
            // If we have an empty namespace...
            if (node.Name.NamespaceName == "")
            {
                // Remove the xmlns='' attribute. Note the use of
                // Attributes rather than Attribute, in case the
                // attribute doesn't exist (which it might not if we'd
                // created the document "manually" instead of loading
                // it from a file.)
                node.Attributes("xmlns").Remove();
                // Inherit the parent namespace instead
                node.Name = node.Parent.Name.Namespace + node.Name.LocalName;
            }
        }
        Console.WriteLine(doc); // Or doc.Save(...)
    }
}

If you add the namespace of the parent element to the element then the empty namespace tag disappears, as it isn't required because the element is in the same namespace.