<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def extract_subject_info_extension(cert_obj):
 """Extract DataONE SubjectInfo XML doc from certificate. Certificates issued by DataONE may include an embedded XML doc containing additional information about the subject specified in the certificate DN. If present, the doc is stored as an extension with an OID specified by DataONE and formatted as specified in the DataONE SubjectInfo schema definition. Args: cert_obj: cryptography.Certificate Returns: str : SubjectInfo XML doc if present, else None """

    try:
        subject_info_der = cert_obj.extensions.get_extension_for_oid(
            cryptography.x509.oid.ObjectIdentifier(DATAONE_SUBJECT_INFO_OID)
        ).value.value
        return str(pyasn1.codec.der.decoder.decode(subject_info_der)[0])
    except Exception as e:
        logging.debug('SubjectInfo not extracted. reason="{}"'.format(e))