Error when transforming config root node containing a namespace

Transforming the root node of a config file that contains a namespace fails with this error: Could not write Destination file: Object reference not set to an instance of an object.

This transform will cause the exception to be thrown:

<?xml version="1.0"?>
<configuration xmlns:config="urn:test:configuration" xmlns:xdt="http://schemas.microsoft.com/XML-Document-Transform" rootAttribute="someValue" xdt:Transform="SetAttributes(rootAttribute)">
  <appSettings>
    <add key="setting01" value="debug01"
         xdt:Locator="Match(key)" xdt:Transform="Replace" />    
    <add key="setting02" value="debug02"
         xdt:Locator="Match(key)" xdt:Transform="Replace" />
  </appSettings>
</configuration>

I think this is related to the Microsoft.Web.Xdt package. The transform executes successfully, but the exception is thrown on document.Save(destination)

    public class Transformer : ITransformer {
        public void Transform(string source, string transform, string destination) {
            if (string.IsNullOrWhiteSpace(source)) { throw new ArgumentNullException("source"); }
            if (string.IsNullOrWhiteSpace(transform)) { throw new ArgumentNullException("transform"); }
            if (string.IsNullOrWhiteSpace(destination)) { throw new ArgumentNullException("destination"); }

            if (!File.Exists(source)) {
                throw new FileNotFoundException("File to transform not found", source);
            }
            if (!File.Exists(transform)) {
                throw new FileNotFoundException("Transform file not found", transform);
            }

            using (XmlTransformableDocument document = new XmlTransformableDocument())
            using (XmlTransformation transformation = new XmlTransformation(transform)) {
                document.PreserveWhitespace = true;
                document.Load(source);

                var success = transformation.Apply(document);
                if (!success) {
                    string message = string.Format(
                        "There was an unknown error trying while trying to apply the transform. Source file='{0}',Transform='{1}', Destination='{2}'",
                        source,transform,destination);
                    throw new TransformFailedException(message);
                }

                // Error occurs here
                // Could not write Destination file: Object reference not set to an instance of an object.
                document.Save(destination);
            }
        }

I downloaded the SlowCheetah project and updated the Microsoft.Web.Xdt nuget package to the latest version. That stopped the error from happening.

I was going to try to fix the project and submit a pull request, but I am not familiar with Nuget package projects or Visual Studio extension projects. SlowCheetah.Xdt.dll has a dependency on an older version of Microsoft.Web.XmlTransform.

sayedihashimi / slow-cheetah

Error when transforming config root node containing a namespace #186