Correct handling for Update-attribute on -r (revert)

CentralisedPackageConverter/PackageConverter.cs

@@ -108,7 +108,14 @@ private void RevertProject(FileInfo project, bool dryRun, Encoding encoding, str
             if( packageReference.Parent is not null )
             {
                 var condition = GetAttributeValue( packageReference.Parent, "Condition" ) ?? string.Empty;
-                var package = GetAttributeValue( packageReference, "Include" );
+                if (!TryGetAttributeValue(packageReference, "Include", out var package))
+                {
+                    if (!TryGetAttributeValue(packageReference, "Update", out package))
+                    {
+                        Console.WriteLine("Package reference has no Include or Update attribute. Skipping...");
+                        continue;
+                    }
+                }
 
                 if( this.referencesByConditionThenName.TryGetValue( condition, out var packagesByName ) )
                 {
@@ -244,6 +251,22 @@ private IEnumerable<XElement> GetDescendants(XDocument xml, string name)
         return attr?.Value;
     }
 
+    /// <summary>
+    /// Try to get an attribute value from an XML Element
+    /// </summary>
+    /// <param name="elem">XML element. If null, result is false.</param>
+    /// <param name="name">Attribute name, checked namespce- and case-insensitive (pick first)</param>
+    /// <param name="value">The attribute value.</param>
+    /// <returns>Boolean whether attribute was picked</returns>
+    private static bool TryGetAttributeValue(XElement? elem, string name, out string? value)
+    {
+        var attr = elem?.Attributes().FirstOrDefault(x =>
+            string.Equals(x.Name.LocalName, name, StringComparison.OrdinalIgnoreCase));
+
+        value = attr?.Value;
+        return value != null;
+    }
+
     /// <summary>
     /// Safely delete attributes with a name.
     /// </summary>