Umbraco Helper: Align GetDictionaryValue nullability with behaviour (closes #21145)

[AndyButland]

Description

#21145 raised a concern about a change in behaviour of the GetDictionaryValue method, retuning empty string instead of null. This doesn't seem to be the case and it's consistent going back to Umbraco 13. However the signature suggests null can be returned, even though the implementation will never return null.

So to align behaviour with the signature I've changed the nullability such that it's clear a null string will never be returned.

Change Summary

• Aligns the return type nullability of ICultureDictionary indexer and UmbracoHelper.GetDictionaryValue methods with actual behaviour
• The implementation already returns an empty string (never null) when no dictionary item is found, but the interface incorrectly declared string?
• Updated XML documentation to clarify the return behaviour

Testing

Visual inspection should suffice here, but you can verify the method still works as expected using an existing and non-existing key:

<div>Exists: @Umbraco.GetDictionaryValue("exists")</div>
<div>Not Exists: @(Umbraco.GetDictionaryValue("notExists") == string.Empty ? "Empty String" : "Something else")</div>

[Copilot]

Pull request overview

This pull request corrects the return type nullability annotations for dictionary value methods to match their actual implementation behavior. The methods have always returned empty strings instead of null when dictionary items are not found, but the type signatures incorrectly declared nullable return types.

Changes:

• Changed ICultureDictionary indexer return type from string? to string
• Changed UmbracoHelper.GetDictionaryValue method return types from string? to string
• Updated XML documentation to explicitly state that empty strings are returned instead of null

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/Umbraco.Core/Dictionary/ICultureDictionary.cs	Updated interface indexer return type to non-nullable string and improved XML documentation
src/Umbraco.Web.Common/UmbracoHelper.cs	Updated GetDictionaryValue method return types to non-nullable string and clarified documentation

Comments suppressed due to low confidence (1)

src/Umbraco.Web.Common/UmbracoHelper.cs:113

• The XML documentation summary is incorrect. This method returns the dictionary value for the specified key, not the dictionary value with a default fallback. The summary should match the behavior described in the returns tag. Consider: "Returns the dictionary value for the key specified".

    /// <summary>
    ///     Returns the dictionary value for the key specified, and if empty returns the specified default fall back value

[Zeegaan]

Looks good to me 🙆‍♂️