merge jsonschema

@SuppressWarnings("unchecked")
private static Document innerJsonSchema(Document full) {
  // full is { "$jsonSchema": { ... } }
  return (Document) full.get("$jsonSchema");
}

private static Document mergeSchemasAsOneOf(Document... fullSchemas) {
  List<Document> versions = new ArrayList<>();
  for (Document full : fullSchemas) {
    versions.add(innerJsonSchema(full));
  }
  return new Document("$jsonSchema", new Document("oneOf", versions));
}

// If you prefer "anyOf":
private static Document mergeSchemasAsAnyOf(Document... fullSchemas) {
  List<Document> versions = new ArrayList<>();
  for (Document full : fullSchemas) {
    versions.add(innerJsonSchema(full));
  }
  return new Document("$jsonSchema", new Document("anyOf", versions));
}