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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 fetch_html_by_subject(self, email_name):
 """ Get the html of an email, searching by subject. @Params email_name - the subject to search for @Returns HTML content of the matched email """

        if not email_name:
            raise EmailException("Subject cannot be null")

        results = self.__imap_search(SUBJECT=email_name)
        sources = self.fetch_html(results)

        return sources