AST Renderer / Comparison not working

[vstange]

It seem our AST Renderer for comparing MathML is currently not working. See:

Detailed Error Information is:

Type:		undefined
Description:		f is null
StatusCode:		undefined

Reproduce
Click "Render" on https://vmext.wmflabs.org/merged-asts.html

Don't know if we still use this example but the problem occurs also from HyPlag out whenever I try to compare two formulas via the the embedded script function. Do we need to handle this differently now? Then we should update our documentation likewise.

Additional context

• occurs on all browsers
• also occurs with our old vmext-demo on: https://vmext-demo.wmflabs.org