fix: tests type errors

app/controllers/click.cr

@@ -16,6 +16,9 @@ module App::Controllers
         env.response.status_code = 301
         env.response.headers.add("Location", url)
         env.response.headers.add("X-Forwarded-For", remote_address)
+        if user_agent = env.request.headers["User-Agent"]?
+          env.response.headers.add("User-Agent", user_agent)
+        end
 
         # non-blocking click proccessing
         spawn do

app/controllers/link.cr

@@ -145,7 +145,7 @@ module App::Controllers
         "data" => items.map { |item| yield item },
         "pagination" => {
           "has_more" => has_more,
-          "next_cursor" => next_cursor
+          "next" => next_cursor
         }
       })
     end

app/lib/controller.cr

@@ -23,7 +23,7 @@ module App::Lib
       missing_fields = required_fields.reject { |field| json_params.has_key?(field) }
 
       unless missing_fields.empty?
-        error_message = missing_fields.join(", ") + " required"
+        error_message = "#{missing_fields.first}: Required field"
         raise App::BadRequestException.new(@env, error_message)
       end