Issues with GpxDataSource

CesiumJS
1

Hi,
I am trying to load a GPX file into the Cesium Viewer with the following code:

   viewer.dataSources
          .add(
            Cesium.GpxDataSource.load(
              "*gpx file path*",
              {
                clampToGround: true,
              }
            )
          )

but it does not work, and the following error is returned:

Uncaught TypeError: Cesium.GpxDataSource is undefined

Do you have any solution for it? Is there something missing?

Thank you!