Fix missing tag suggestions when no culture available.

[BenWhite27]

Prerequisites

• I have added steps to test this contribution in the description below

Fixes: #19693

Description

As per issue description, when the Tags property editor is used inside an umb-property-dataset element the culture provided to the property editor is null.

I found that culture is not required by the Tag's Repository, Data Source, or Management API. So, the check for undefined value is not needed. I've modified the code to replace undefined values with null which can be handled by the subsequent call chain.

I've tested this by modifying the dashboard-with-property-dataset example with the following additions (not committed)

Added additional property to data set.

data: UmbPropertyValueData[] = [
    {
        alias: 'textProperty',
        value: 'Hello',
    },
    {
        alias: 'tagsProperty',
        value: [],
    }];

Added the tags property editor to the dashboard with configuration

<umb-property
    label="Tags"
    description="Tags editor for testing"
    alias="tagsProperty"
    property-editor-ui-alias="Umb.PropertyEditorUi.Tags"
    .config=${
	[{
	    "alias": "group",
	    "value": "Fruits"
	}]
    }></umb-property>

[github-actions]

Hi there @BenWhite27, thank you for this contribution! 👍

While we wait for one of the Core Collaborators team to have a look at your work, we wanted to let you know about that we have a checklist for some of the things we will consider during review:

• It's clear what problem this is solving, there's a connected issue or a description of what the changes do and how to test them
• The automated tests all pass (see "Checks" tab on this PR)
• The level of security for this contribution is the same or improved
• The level of performance for this contribution is the same or improved
• Avoids creating breaking changes; note that behavioral changes might also be perceived as breaking
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[Copilot]

Pull Request Overview

This PR ensures tag suggestions still load when no culture is provided by removing the undefined guard and defaulting culture to null in the repository call.

• Removed the culture === undefined check so suggestions aren’t skipped when culture is missing
• Used the nullish coalescing operator to pass null for culture instead of undefined

Comments suppressed due to low confidence (2)

src/Umbraco.Web.UI.Client/src/packages/tags/components/tags-input/tags-input.element.ts:76

• Consider adding a unit test for the scenario where culture is undefined to verify that passing null still returns the expected tag suggestions.

		const { data } = await this.#repository.queryTags(this.group, this.culture ?? null, query);

src/Umbraco.Web.UI.Client/src/packages/tags/components/tags-input/tags-input.element.ts:74

• Add or update a comment/docstring to note that culture is now optional and will be defaulted to null when missing.

	async #getExistingTags(query: string) {

[AndyButland]

Thanks very much @BenWhite27. I've tested this out and can confirm it works as expected, both in the examples and in the backoffice itself when editing a tags property.