Postmark Cc email address can not be looped over if empty

When a postmark Cc email address is empty we can not loop over the result without getting an exception.

Anymail version: 9.1
ESP (Mailgun, SendGrid, etc.): postmark
Versions of Django, requests, python: django 4.2
Exact error message and/or stack trace

Below you can find an minimal example using parts of the codebase:

# This is how an empty cc looks in the esp_event from postmark
In [12]: esp_event = {"ccFull": []}

# This is how it is processed in anymail
# https://github.com/anymail/django-anymail/blob/main/anymail/webhooks/postmark.py#L183
In [13]: cc=", ".join([self._address(cc) for cc in esp_event.get("CcFull", [])])

# Now we are left with an empty string
In [14]: cc
Out[14]: ''

# After constructing the message it remains an empty string
In [15]: message = AnymailInboundMessage.construct(cc=cc)

# If you then try to loop over the cc email addresses in the message you get an exception
In [16]: [print(x) for x in message.cc]
---------------------------------------------------------------------------
AnymailInvalidAddress                     Traceback (most recent call last)
Cell In[16], line 1
----> 1 [print(x) for x in message.cc]

File /opt/venv/lib/python3.10/site-packages/anymail/inbound.py:72, in AnymailInboundMessage.cc(self)
     70 """list of EmailAddress objects from Cc header"""
     71 # equivalent to Python 3.2+ message['Cc'].addresses
---> 72 return self.get_address_header("Cc")

File /opt/venv/lib/python3.10/site-packages/anymail/inbound.py:116, in AnymailInboundMessage.get_address_header(self, header)
    114 values = self.get_all(header)
    115 if values is not None:
--> 116     values = parse_address_list(values)
    117 return values or []

File /opt/venv/lib/python3.10/site-packages/anymail/utils.py:170, in parse_address_list(address_list, field)
    168         if len(parsed) > len(address_list):
    169             errmsg += " (Maybe missing quotes around a display-name?)"
--> 170         raise AnymailInvalidAddress(errmsg)
    172 return parsed

AnymailInvalidAddress: Invalid email address '' parsed from ''.

I would expect that .cc is set to [] in case no cc email address is set on the incoming message. Is this indeed a bug or are my expectations not correct? Also I would not expect that parsing errors occur after the parsing procedure.

Let me know what you think.

anymail / django-anymail

Postmark Cc email address can not be looped over if empty #307