Fixes a NullReferenceException bug when the ValueSetValidator is null

[Shazwazza]

Fixes a bug where the ValueSetValidator is null which will cause a NullReferenceException.

Prerequisites

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

Description

When creating a custom index based on Umbraco content/media via this code:

services.AddExamineLuceneIndex<UmbracoContentIndex, ConfigurationEnabledDirectoryFactory>("TestIndex");

It will mean that this index's LuceneDirectoryIndexOptions.ValueSetValidator will be null and when rebuilding the index, a null reference exception will occur.

To resolve this, it is required that an explicit value set validator is applied to the options, like:

public class LuceneEditorialIndexOptions : IConfigureNamedOptions<LuceneDirectoryIndexOptions>
{
    private readonly IUmbracoIndexConfig _umbracoIndexConfig;

    public LuceneEditorialIndexOptions(IUmbracoIndexConfig umbracoIndexConfig)
    {
        _umbracoIndexConfig = umbracoIndexConfig;
    }

    public void Configure(string? name, LuceneDirectoryIndexOptions options)
    {
        if (name?.Equals("EditorialIndex") is false)
        {
            return;
        }

        options.Validator = _umbracoIndexConfig.GetContentValueSetValidator();
    }

    // not used
    public void Configure(LuceneDirectoryIndexOptions options) => throw new NotImplementedException();
}

However, it is not clear that this is a requirement but either way, a null reference exception shouldn't be thrown.

A reference: SDKits/ExamineX#103 (comment)

[github-actions]

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

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[georgebid]

Hey @Shazwazza! Thanks a lot for your PR, someone on the core collaborators team will review this soon 😸

[Matthew-Wise]

Hi @Shazwazza

Confirmed working and what a sneaky bug, from a user point of view it all works but you can see the null ref in the logs.

Thanks
Matt