Fix: change folder info data name column to nullable

src/main/java/com/example/kdan_data_center/datacenter/folder/data/FolderInfoData.kt

@@ -11,7 +11,7 @@ data class FolderInfoData(
     data class Folder(
             @SerializedName("id") val id: Int,
             @SerializedName("user_id") val userId: Int,
-            @SerializedName("folder_name") val folderName: String,
+            @SerializedName("folder_name") val folderName: String?,
             @SerializedName("created_at") val createdAt: String,
             @SerializedName("updated_at") val updatedAt: String,
             @SerializedName("is_deleted") val isDeleted: Boolean,