code: function getMissingVars(flurQL, opts) {
    const vars = flurQL.vars;
  
    if (!vars || !Array.isArray(vars)) {
      return [];
    }
  
    if (opts && opts.vars) {
      return vars.filter((v) => { return !opts.vars[v]; });
    } else {
      return vars;
    }
  }
docs: given a query and options, returns a vector of variables that were not provided via options. We use this to look for the variables in props