#vulnerable code 
                             private <T> String buildResourceName(T entity) {
		FirestorePersistentEntity<?> persistentEntity =
				this.mappingContext.getPersistentEntity(entity.getClass());
		FirestorePersistentProperty idProperty = persistentEntity.getIdPropertyOrFail();
		Object idVal = persistentEntity.getPropertyAccessor(entity).getProperty(idProperty);

		return buildResourceName(persistentEntity, idVal.toString());
	} 
                            #location 7 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                             private <T> String buildResourceName(T entity) {
		FirestorePersistentEntity<?> persistentEntity =
				this.mappingContext.getPersistentEntity(entity.getClass());
		FirestorePersistentProperty idProperty = persistentEntity.getIdPropertyOrFail();
		Object idVal = persistentEntity.getPropertyAccessor(entity).getProperty(idProperty);
		if (idVal == null) {
			if (idProperty.getType() != String.class) {
				throw new FirestoreDataException(
								"ID property was null; automatic ID generation is only supported for String type");
			}

			//TODO: replace with com.google.cloud.firestore.Internal.autoId() when it is available
			idVal = AutoId.autoId();
			persistentEntity.getPropertyAccessor(entity).setProperty(idProperty, idVal);
		}
		return buildResourceName(persistentEntity, idVal.toString());
	}