thymeleaf th:text displays "" in each variable

I'm trying to display a json data into an HTML table. but I found that every table's contents contain a "..." in each variable, like this:

table view

I want the "..." sign of each variable to disappear. here is my code:

The controller method:

@GetMapping()
    fun home(model: Model): String {

        val users = userService.getAllUsers()

        model.addAttribute("tableAttributes", jsonHelper.getMembersKeyValues(User()))
        model.addAttribute("tableData", users.map { jsonHelper.getSeparatedMembersByKeys(it) })

        return "home"
    }

Here is the HTML:

<div class="container-sm">
    <table class="table">
        <thead>
        <tr>
            <th scope="col" th:each="attribute: ${tableAttributes}" th:text="${attribute}">#</th>
        </tr>
        </thead>
        <tbody>
        <tr th:each="data: ${tableData}">
            <td th:each="variable: ${data}" th:text="${variable}"></td>
        </tr>
        </tbody>
    </table>
</div>

The JsonHelper class:

@Component
class JsonHelper() {

    private val gson = Gson().newBuilder().serializeNulls().create()

    fun <T> toJsonObject(model: T): JsonObject {
        val jsonString = gson.toJson(model)
        return gson.fromJson(jsonString, JsonObject::class.java)
    }

    fun <T> getMembersKeyValues(model: T): List<String> {
        val jsonObject = toJsonObject(model)
        return jsonObject.keySet().toList()
    }

    fun <T> getSeparatedMembersByKeys(model: T): JsonArray {
        val jsonObject = toJsonObject(model)
        val keys = jsonObject.keySet().toList()

        val data = JsonArray()

        for (key in keys) {
            data.add(jsonObject.get(key))
        }
        return data
    }

}

I use dummy data like this:

data class User(
    var username: String? = null,
    var password: String? = null
): Serializable