Returns True iff this issue was closed after given date. If after not given, only checks if issue is closed.

def closed_issue(issue, after=None):
    """Returns True iff this issue was closed after given date. If after not given, only checks if issue is closed."""
    if issue['state'] == 'closed':
        if after is None or parse_timestamp(issue['closed_at']) > after:
            return True
    return False