fix: prevent NullPointerException in Page.buildNextGenPage

[Nepomuk5665]

Summary

This PR fixes a potential NullPointerException in the Page.buildNextGenPage method that can occur when parsing JSON responses from next-gen API endpoints.

Bug Description

In buildNextGenPage, the code retrieves JsonNode values from the meta object and calls .isNull() on them without first checking if they are null:

JsonNode nextPageNode = meta.get("next_page_url");
if (!nextPageNode.isNull()) {  // NPE if nextPageNode is null
    builder.nextPageUrl(nextPageNode.asText());
}

The meta.get("key") method returns Java null when the key doesn't exist in the JSON. Calling .isNull() on a null reference throws NullPointerException.

Fix

Added null checks before calling .isNull(), following the same pattern already used in the buildPage method:

JsonNode nextPageNode = meta.get("next_page_url");
if (nextPageNode != null && !nextPageNode.isNull()) {
    builder.nextPageUrl(nextPageNode.asText());
}

Affected Fields

• next_page_url
• previous_page_url
• first_page_url
• page_size

All four fields now have proper null checks.

Testing

The fix follows the existing pattern in buildPage (lines 153-173) which correctly handles this case.