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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def ensure_regex_namespace(self, keyword: str, pattern: str) -> Namespace: """Get or create a regular expression namespace. :param keyword: The keyword of a regular expression namespace :param pattern: The pattern for a regular expression namespace """

        if pattern is None:
            raise ValueError('cannot have null pattern')

        namespace = self.get_namespace_by_keyword_pattern(keyword, pattern)

        if namespace is None:
            log.info('creating regex namespace: %s:%s', keyword, pattern)
            namespace = Namespace(
                keyword=keyword,
                pattern=pattern
            )
            self.session.add(namespace)
            self.session.commit()

        return namespace