Adding Scala Nature

Hey guys,
I'm writing a small plugin to add Scala Nature to a Java project, I'm pretty
much trying to do the same thing the Scala plugin does in the
scala.tools.eclipse.ToggleScalaNatureAction.scala class:

private void addScalaNature(IProject project)
{
try {
IProjectDescription description = project.getDescription();
String[] natures = description.getNatureIds();
String[] newNatures = new String[natures.length + 1];
System.arraycopy(natures, 0, newNatures, 1, natures.length);
newNatures[0] = "org.eclipse.jdt.core.scalabuilder";
for(String str: newNatures)
{
System.out.println(str);
}
description.setNatureIds(newNatures);
project.setDescription(description, null);
//project.touch(null);
} catch (CoreException e) {
// Something went wrong
}

}

But my code doesnt seem to add Scala Nature, the old nature remains... Can
someone please tell me whats wrong?

Thank you.