Changes

     for _, var_name in ipairs(must_have) do

     for _, var_name in ipairs(must_have) do

         if self._args[var_name] == nil then

         if self._args[var_name] == nil then

             error("\"" .. var_name .. "\" must be provided. Please double-check that you have this variable and that it is spelled correctly.")

             error("\"" .. var_name .. "\" must be provided. Please double-check that you have this variable and that it is spelled correctly")

         end

         end

     end

     end