Handle nullable properties

[gcatanese]

This pull request adds support for explicit null serialization in the Management API classes, allowing clients to control whether attributes with null values are included in the JSON payload.

The default behavior doesn't change: null attributes are not included in the JSON requests. However, developers can override the logic by customizing the request object:

• set includeNullValues as true
• set explicitly the attribute(s) as null

TerminalSettings terminalSettings = new TerminalSettings();
    terminalSettings
        .includeNullValues(true)
        .connectivity(new Connectivity().simcardStatus(Connectivity.SimcardStatusEnum.ACTIVATED))
        .setSurcharge(null);

The changes introduce new flags and helper methods to track when attributes are explicitly set to null. This is done by introducing a state (boolean flag) that it is marked as true when the attribute is modified.
Attributes initialised as null are not considered updated and it will not included in the serialization.

This improves API flexibility and consistency, especially for partial updates or PATCH requests.

These changes ensure that API consumers have fine-grained control over the inclusion of null values in their requests, which is important for partial updates (i.e. update TerminalSettings) and for conforming to various API contract requirements.

Other changes

The Management API models have been regenerated to implement the new Mustache templates, meanwhile the Management API OpenAPI spec has changed, therefore there are other changes:

• AffirmInfo add pricePlan attribute
• PaymentMethod add support for Givex, Scs, Valuelink
• PaymentMethodResponse add support for Klarna_b2b, Givex, Scs, Valuelink
• PaymentMethodSetupInfo add support for Klarna_b2b, Givex, Scs, Valuelink
• TerminalSettings add support for Moto
• UpdatePaymentMethodInfo deprecate storeIds attribute

Fix #1584

[gemini-code-assist]

Summary of Changes

Hello @gcatanese, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the API's flexibility by introducing explicit null serialization across all model classes. Previously, null attributes were omitted from JSON requests by default. With this change, clients can now explicitly include null values in their JSON payloads by setting an includeNullValues flag and explicitly setting attributes to null. This functionality is particularly beneficial for scenarios involving partial updates or PATCH requests, ensuring greater control and consistency with various API contract requirements.

Highlights

• Explicit Null Serialization: Introduced support for explicit null serialization in all model classes, allowing clients to control whether attributes with null values are included in JSON payloads.
• New Flags and Helper Methods: Added isSet boolean flags for each property to track if an attribute has been explicitly set, along with an includeNullValues flag and a getExplicitNulls() method utilizing @JsonAnyGetter for conditional null serialization.
• API Flexibility: This enhancement improves API flexibility and consistency, particularly for handling partial updates and PATCH requests, by giving developers fine-grained control over null value inclusion.
• Model Simplification: The DeviceInfo.java model was refactored to remove several fields, streamlining its structure and focusing on core device information.

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[gemini-code-assist]

Code Review

This pull request introduces a mechanism to explicitly serialize null values in model classes, which provides more control over the generated JSON payload. The implementation adds includeNullValues and isSet<Property> flags to track state, along with a @JsonAnyGetter method getExplicitNulls to handle the serialization.

While the approach is functional, I've identified significant code duplication, particularly with the addIfNull helper method and the boilerplate for includeNullValues handling, which are repeated in every modified model. I've left a comment suggesting the use of a base class or utility class to centralize this logic, which would greatly improve maintainability.

Additionally, I've suggested an alternative to using individual isSet<Property> boolean flags by using a single Set<String> to track set properties, which would reduce the number of fields and simplify the models.

Finally, I've flagged a potentially breaking change in the DeviceInfo class where several fields have been removed. This should be reviewed to ensure it is intentional.

Overall, the changes achieve the goal of handling nullable properties, but there are opportunities to refactor for better code quality and long-term maintenance.