diffenator2 creating blank report on variable color font with custom axes

if I run diffenator2 on my variable colorv0 font with custom variation axes
``` 
diffenator2 proof my-variable-color-font.ttf -out out/proof 

``` 
only a blank html page is created with following syntax
```
<p><a href='diffenator2-report.html'>diffenator2-report.html</a></p>
``` 
and no proof files is generated