fixing NPE

[jkiddo]

This pull request updates how R4 and R4B exclusions are handled during the IG loading process. Instead of immediately marking exclusions as they are parsed, the exclusions are now collected and processed together later in the loading sequence. This change improves code clarity and separation of concerns.

Refactoring of exclusion handling:

• Added r4Exclusions and r4bExclusions lists to the PublisherFields class to collect exclusion values during parsing, instead of directly marking them.
• Updated the IG loader to add exclusion values to these new lists instead of calling markExempt immediately.

Processing exclusions during loading:

• Modified the loading process to iterate through the collected exclusions and call markExempt for each, ensuring all exclusions are processed together at the appropriate stage.

[grahamegrieve]

ok