protected createVisual(context: IRenderContext, port: IPort): Visual | null {
const ellipseElement = document.createElementNS(
'http://www.w3.org/2000/svg',
'ellipse'
)
const { x, y } = port.location
ellipseElement.setAttribute('cx', String(x))
ellipseElement.setAttribute('cy', String(y))
ellipseElement.setAttribute('rx', '3')
ellipseElement.setAttribute('ry', '3')
ellipseElement.setAttribute('fill', '#6c9f44')
ellipseElement.setAttribute('stroke', '#e6f8ff')
ellipseElement.setAttribute('stroke-width', '1')
return new SvgVisual(ellipseElement)
}