Accessing site.data in custom tag/plugin

1

I’m trying to access data in site.data from a custom Liquid tag that I’ve created. I’m not sure how to do it. I’ve copied below what I have tried to do, but I get the error:

  Liquid Exception: undefined method `registers' for nil:NilClass @definition = @context.registers[:site].data.terminology["{@category}"]['definition'] ^^^^^^^^^^ in ...

module Jekyll
    class Term < Liquid::Tag
        def initialize(tag_name, input, tokens)
            super
            vars = input.split(" ")
            @term = vars[0]
            @category = vars[1]
        end
        
        def render(context)
            @definition = @context.registers[:site].data.terminology["{@category}"]['definition']
            "#{@definition}"
        end
    end
end

Liquid::Template.register_tag('term', Jekyll::Term)

I’m rather new to ruby so please excuse my inexperience.