Ignore the `size` since a complete line must be processed.

def readline(self, size=-1):
        "Ignore the `size` since a complete line must be processed."
        while True:
            try:
                record = next(self.reader)
            except StopIteration:
                break

            # Ensure this is a valid record
            if checks.record_is_valid(record):
                if self.use_cache:
                    # Ensures the cache is updated and available
                    self.variants.ensure_cache(record)

                # Calculate the MD5 of the variant itself (not the record)
                md5 = calculate_md5(record)

                # Ensure this variant is not already loaded
                if not self.use_cache or md5 not in self.variants:
                    cleaned = self.process_line(record)
                    cleaned.append(md5)
                    return self.outdel.join(cleaned) + '\n'

        return ''