Node SVG not displaying after customization

I was trying to follow the example codes to customize the node appearance.
I have following code:
```javascript
var graphics = Viva.Graph.View.webglGraphics();
graphics.node(function(node) {
console.log(node.id);
return Viva.Graph.svg("rect")
.attr("width", 10)
.attr("height", 10)
.attr("fill", "#00a2e8");
});

// specify where it should be rendered:
var renderer = Viva.Graph.View.renderer(graph, {
container: document.getElementById('graphDiv'),
layout : layout,
graphics: graphics,
renderLinks : true
});
renderer.run();
```
and nodes disappear:


Removing graphics.node(... reveals the nodes again:


Behind Viva.Graph.svg("rect") is a valid object.

Start by reproducing the example with Viva.Graph.View.webglGraphics(), graphics.node(), Viva.Graph.svg("rect"), and renderer.run(). Trace how the customized SVG node is handled by the WebGL graphics path; done means customized rectangular nodes render in graphDiv while links still display.

Written by the indexing model from the issue text.