If you do not want to see 'Tags: (none)' for tasks that do not have any tags, you can choose to hide this in your Preferences.

Set the 'Tags display' option to 'Hide if no tags', and tags will only be shown if they exist for the task or note.

When this is set, you will see a Edit Tag icon appear when you move the mouse over a task or note that does not have tags. Click this icon to show the edit tag form.