The ccUtil apex class provides two methods to check the input or return data of the Global API's: ccrz.ccUtil.isNotEmpty(Map<String, Object>) and ccrz.ccUtil.isEmpty(Map<String, Object>). These methods return true if the map is not null and contains at least one entry, or if the map is null or empty, respectively. Similarly, ccrz.ccUtil.isNotEmpty(List<Object>) and ccrz.ccUtil.isEmpty(List<Object>) return true if the list is not null and contains at least one element, or if the list is null or empty, respectively. These methods are useful for validating the input parameters or the output results of the Global API's.

Explanation
To ensure that a custom field is available to display on a given page, the Developer needs to override the Service Class that the page uses and update the Service Management in CCAdmin for the given storefront to use this new Service Class. The Service Class is responsible for retrieving and setting data for a given page.
The Logic Class is responsible for implementing business logic and validation rules for a given page. Creating a new Service Class or Logic Class is not necessary, as overriding an existing one can achieve the same result.
Salesforce References: B2B Commerce and D2C Commerce Developer Guide, Service Classes, Logic Classes

To help troubleshoot and respond to actions in checkout, the developer's code should listen for CommerceDiagnosticEvents. CommerceDiagnosticEvents is an event that is fired by Salesforce B2B Commerce when an error occurs in the storefront. CommerceDiagnosticEvents contains information about the error, such as error code, error message, error type, and error details. CommerceDiagnosticEvents can be subscribed by other components or services that want to handle or display the error information in different ways. The developer's code can listen for CommerceDiagnosticEvents using an aura:handler tag in Aura Components or an @wire decorator in Lightning web components. The developer's code can also use the event information to perform custom logic or actions based on the error, such as logging, reporting, or notifying. CommerceBubbleEvents is not an event that the developer's code should listen for in checkout, as it is not related to troubleshooting or responding to actions. CommerceBubbleEvents is an event that is fired by Salesforce B2B Commerce when a user interacts with a bubble component in the storefront. A bubble component is a user interface element that displays information or options in a pop-up window when clicked or hovered over. CommerceBubbleEvents contains information about the user interaction, such as bubble name, bubble type, and bubble value. CommerceErrorEvents is not an event that the developer's code should listen for in checkout either, as it is not related to troubleshooting or responding to actions. CommerceErrorEvents is an event that is fired by Salesforce B2B Commerce when a validation error occurs in the storefront. CommerceErrorEvents contains information about the validation error, such as field name, field label, and error message. CommerceActionEvents is not an event that the developer's code should listen for in checkout either, as it is not related to troubleshooting or responding to actions. CommerceActionEvents is an event that is fired by Salesforce B2B Commerce when a user performs an action in the storefront. CommerceActionEvents contains information about the user action, such as action name, action type, and action parameters. Salesforce Reference: B2B Commerce Developer Guide: Handle Errors, B2B Commerce Developer Guide: Handle User Interactions with Bubble Components, B2B Commerce Developer Guide: Handle Validation Errors, B2B Commerce Developer Guide: Handle User Actions