I've just uploaded version 1.1. The previous version was expecting a string as a param for expressions. It worked well with numeric variables but could bring problems with various other attempts like using other expression (that returns int) as a param.
Even though it's a super small fix I couldn't get it working (backward compatible) by setting the old expressions as deprecated for some reason so I had to make it as non-fully-backward compatible (still the link to the old version is available).
If you used this plugin in your project and provided a string as a parameter for expression, then you will have to remove that line from C2, update the plugin, restart C2 and add it again.
If you haven't used a string earlier then you can simply update the plugin. Sorry for this issue, I just missed this detail somehow.