presto-spi/src/main/java/io/prestosql/spi/connector/FixedPageSource.java/FixedPageSource/getNextPage
class FixedPageSource:    @Override
    public Page getNextPage()
    {
        if (isFinished()) {
            return null;
        }
        Page page = pages.next();
        completedBytes += page.getSizeInBytes();
        return page;
    }