So I've been using the Revit 2026 API ( and .NET ) to make QoL stuff in an addIn.

I wanted to create some Bezier Curves (HermitSplines) and store the newly created element for later use.

Here is the function I use :

        public DetailCurve CreateBezierCurve(Document document, List points, XYZ tangent0, XYZ tangent3)
        {
            DetailCurve result;
            var view = document.ActiveView;

            HermiteSpline spline = HermiteSpline.Create(
                points,
                false,
                new HermiteSplineTangents()
                { 
                    StartTangent = tangent0,
                    EndTangent = tangent3
                }
            );

            using (Transaction tx = new Transaction(document, "Create Bezier Curve"))
            {
                tx.Start();
                result = document.Create.NewDetailCurve(view, spline);
                tx.Commit();
            }

            return result;
        }

The official api info and the IDE helper tab state that the output is indeed a DetailCurve.

It also state that it can return null if a crash appears internally. however I do get the curve created in my file and no sign of any error.

I wonder if this is some bug in the API, or a mistake in the documentation. I could not find anything on that subject.

Any help or info is welcome. Thanks

PS: I know I could find that newly created curve in other ways but it is definitly not as clean as the intended way.

For instance the said curve after creation :