# Buggy code
def _regex_to_static(src, regex):
    """
    Expand regular expression to static match.
    """
    if not src or not regex:
        return None

    try:
        src = re.search(regex, src)
    except Exception as ex:
        raise CommandExecutionError("{0}: '{1}'".format(ex.message, regex))

    return src and src.group() or regex


# Traceback (TypeError)
[root@saltminion1 ~]# salt-minion -ldebug
[DEBUG   ] Reading configuration from /etc/salt/minion
[DEBUG   ] Including configuration from '/etc/salt/minion.d/_schedule.conf'
[DEBUG   ] Reading configuration from /etc/salt/minion.d/_schedule.conf
[DEBUG   ] Configuration file path: /etc/salt/minion
[WARNING ] Insecure logging configuration detected! Sensitive data may be logged.
[INFO    ] Setting up the Salt Minion "minion1"
[DEBUG   ] Created pidfile: /var/run/salt-minion.pid
[DEBUG   ] Reading configuration from /etc/salt/minion
[DEBUG   ] Including configuration from '/etc/salt/minion.d/_schedule.conf'
[DEBUG   ] Reading configuration from /etc/salt/minion.d/_schedule.conf
[DEBUG   ] The `lspci` binary is not available on the system. GPU grains will not be available.
[WARNING ] IMPORTANT: Do not use md5 hashing algorithm! Please set "hash_type" to sha256 in Salt Minion config!
[INFO    ] The Salt Minion is starting up
[INFO    ] Minion is starting as user 'root'
[DEBUG   ] AsyncEventPublisher PUB socket URI: ipc:///var/run/salt/minion/minion_event_c5a7daa544_pub.ipc
[DEBUG   ] AsyncEventPublisher PULL socket URI: ipc:///var/run/salt/minion/minion_event_c5a7daa544_pull.ipc
[INFO    ] Starting pub socket on ipc:///var/run/salt/minion/minion_event_c5a7daa544_pub.ipc
[INFO    ] Starting pull socket on ipc:///var/run/salt/minion/minion_event_c5a7daa544_pull.ipc
[DEBUG   ] Minion 'minion1' trying to tune in
[INFO    ] Got list of available master addresses: ['192.168.50.11', '192.168.50.12']
[DEBUG   ] Initializing new AsyncAuth for ('/etc/salt/pki/minion', 'minion1', 'tcp://192.168.50.11:4506')
[DEBUG   ] Generated random reconnect delay between '1000ms' and '11000ms' (8729)
[DEBUG   ] Setting zmq_reconnect_ivl to '8729ms'
[DEBUG   ] Setting zmq_reconnect_ivl_max to '11000ms'
[DEBUG   ] Initializing new AsyncZeroMQReqChannel for ('/etc/salt/pki/minion', 'minion1', 'tcp://192.168.50.11:4506', 'clear')
[INFO    ] Master 192.168.50.11 could not be reached, trying next master (if any)
[WARNING ] Master ip address changed from 192.168.50.11 to 192.168.50.12
[DEBUG   ] Initializing new AsyncAuth for ('/etc/salt/pki/minion', 'minion1', 'tcp://192.168.50.12:4506')
[DEBUG   ] Generated random reconnect delay between '1000ms' and '11000ms' (10183)
[DEBUG   ] Setting zmq_reconnect_ivl to '10183ms'
[DEBUG   ] Setting zmq_reconnect_ivl_max to '11000ms'
[DEBUG   ] Initializing new AsyncZeroMQReqChannel for ('/etc/salt/pki/minion', 'minion1', 'tcp://192.168.50.12:4506', 'clear')
[INFO    ] Master 192.168.50.12 could not be reached, trying next master (if any)
[ERROR   ] No master could be reached or all masters denied the minions connection attempt.
[INFO    ] The Salt Minion is shut down
[WARNING ] /usr/lib/python2.7/site-packages/salt/scripts.py:83: DeprecationWarning: BaseException.message has been deprecated as of Python 2.6
log.error('Minion failed to start: {0}'.format(exc.message), exc_info=True)

[ERROR   ] Minion failed to start: 'NoneType' object is not iterable
Traceback (most recent call last):
File "/usr/lib/python2.7/site-packages/salt/scripts.py", line 81, in minion_process
minion.start()
File "/usr/lib/python2.7/site-packages/salt/cli/daemons.py", line 320, in start
self.minion.tune_in()
File "/usr/lib/python2.7/site-packages/salt/minion.py", line 1699, in tune_in
self.sync_connect_master()
File "/usr/lib/python2.7/site-packages/salt/minion.py", line 760, in sync_connect_master
raise six.reraise(*future_exception)
File "/usr/lib64/python2.7/site-packages/tornado/gen.py", line 879, in run
yielded = self.gen.send(value)
File "/usr/lib/python2.7/site-packages/salt/minion.py", line 767, in connect_master
master, self.pub_channel = yield self.eval_master(self.opts, self.timeout, self.safe)
TypeError: 'NoneType' object is not iterable
[WARNING ] ** Restarting minion **
[INFO    ] Sleeping random_reauth_delay of 8 seconds
[DEBUG   ] Reading configuration from /etc/salt/minion
[DEBUG   ] Including configuration from '/etc/salt/minion.d/_schedule.conf'
[DEBUG   ] Reading configuration from /etc/salt/minion.d/_schedule.conf
[DEBUG   ] Configuration file path: /etc/salt/minion
[WARNING ] Insecure logging configuration detected! Sensitive data may be logged.
[INFO    ] Setting up the Salt Minion "minion1"
[DEBUG   ] Created pidfile: /var/run/salt-minion.pid
[DEBUG   ] Reading configuration from /etc/salt/minion
[DEBUG   ] Including configuration from '/etc/salt/minion.d/_schedule.conf'
[DEBUG   ] Reading configuration from /etc/salt/minion.d/_schedule.conf
[DEBUG   ] The `lspci` binary is not available on the system. GPU grains will not be available.
[WARNING ] IMPORTANT: Do not use md5 hashing algorithm! Please set "hash_type" to sha256 in Salt Minion config!
[INFO    ] The Salt Minion is starting up

# Fixed code
def _regex_to_static(src, regex):
    """
    Expand regular expression to static match.
    """
    if not src or not regex:
        return None

    try:
        src = re.search(regex, src)
    except Exception as ex:
        raise CommandExecutionError("{0}: '{1}'".format(_get_error_message(ex), regex))

    return src and src.group() or regex