diff --git a/last_commit.txt b/last_commit.txt
index c56736f95a..f0d53bdfb2 100644
--- a/last_commit.txt
+++ b/last_commit.txt
@@ -1,15 +1,34 @@
-Repository: plone.volto
+Repository: plone.event
 
 
-Branch: refs/heads/main
-Date: 2023-01-12T09:03:00+01:00
-Author: Timo Stollenwerk (tisto) <tisto@users.noreply.github.com>
-Commit: https://github.com/plone/plone.volto/commit/7e16d711ec92185d1315826e113b36a9995511b5
+Branch: refs/heads/master
+Date: 2023-01-13T10:30:30+01:00
+Author: Gogo Bernhard (gogobd) <g.bernhard@akbild.ac.at>
+Commit: https://github.com/plone/plone.event/commit/5ffb4469175d5fa404adf1e716abefad119b8ae3
 
-Update architectural diagram "Plone" -&gt; "Plone core"
+Fixing #13
 
 Files changed:
-M README.rst
+A news/13.bugfix
+M plone/event/utils.py
 
-b'diff --git a/README.rst b/README.rst\nindex 5930344..06ab223 100644\n--- a/README.rst\n+++ b/README.rst\n@@ -77,7 +77,7 @@ Architectural Diagram of Plone 6::\n     \xe2\x94\x82\xe2\x94\x82         plone.volto        \xe2\x94\x82\xe2\x94\x82\n     \xe2\x94\x82\xe2\x94\x94\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x98\xe2\x94\x82\n     \xe2\x94\x82\xe2\x94\x8c\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x90 \xe2\x94\x8c\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x90\xe2\x94\x82\n-    \xe2\x94\x82\xe2\x94\x82   Plone    \xe2\x94\x82 \xe2\x94\x82   Add-Ons   \xe2\x94\x82\xe2\x94\x82\n+    \xe2\x94\x82\xe2\x94\x82 Plone Core \xe2\x94\x82 \xe2\x94\x82   Add-Ons   \xe2\x94\x82\xe2\x94\x82\n     \xe2\x94\x82\xe2\x94\x94\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x98 \xe2\x94\x94\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x98\xe2\x94\x82\n     \xe2\x94\x94\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x80\xe2\x94\x98\n \n'
+b'diff --git a/news/13.bugfix b/news/13.bugfix\nnew file mode 100644\nindex 0000000..5bbd512\n--- /dev/null\n+++ b/news/13.bugfix\n@@ -0,0 +1 @@\n+Fixing issue #13\n\\ No newline at end of file\ndiff --git a/plone/event/utils.py b/plone/event/utils.py\nindex e7681f8..0763205 100644\n--- a/plone/event/utils.py\n+++ b/plone/event/utils.py\n@@ -9,16 +9,16 @@\n import time\n \n \n-DSTADJUST = \'adjust\'\n-DSTKEEP = \'keep\'\n-DSTAUTO = \'auto\'\n+DSTADJUST = "adjust"\n+DSTKEEP = "keep"\n+DSTAUTO = "auto"\n MAX32 = int(2**31 - 1)\n \n-logger = logging.getLogger(\'plone.event\')\n+logger = logging.getLogger("plone.event")\n \n \n def validated_timezone(timezone, fallback=None):\n-    """ Validate a given timezone identifier. If a fallback is given, return it\n+    """Validate a given timezone identifier. If a fallback is given, return it\n         when the given timezone is not a valid pytz zone. Else raise an\n         ValueError exception.\n \n@@ -59,8 +59,8 @@ def validated_timezone(timezone, fallback=None):\n     except Exception:\n         if fallback:\n             logger.warn(\n-                \'The timezone {0} is not a valid timezone from the \'\n-                \'Olson database or pytz. Falling back to {1}.\'.format(\n+                "The timezone {0} is not a valid timezone from the "\n+                "Olson database or pytz. Falling back to {1}.".format(\n                     timezone,\n                     fallback,\n                 )\n@@ -68,61 +68,61 @@ def validated_timezone(timezone, fallback=None):\n             return fallback\n         else:\n             raise ValueError(\n-                \'The timezone {0} is not a valid timezone from \'\n-                \'the Olson database or pytz.\'.format(timezone)\n+                "The timezone {0} is not a valid timezone from "\n+                "the Olson database or pytz.".format(timezone)\n             )\n \n \n-def default_timezone(fallback=\'UTC\'):\n-    """ Retrieve the timezone from the server.\n-        Default Fallback: UTC\n+def default_timezone(fallback="UTC"):\n+    """Retrieve the timezone from the server.\n+    Default Fallback: UTC\n \n-        :param fallback: A fallback timezone identifier.\n-        :type fallback: string\n+    :param fallback: A fallback timezone identifier.\n+    :type fallback: string\n \n-        :returns: A timezone identifier.\n-        :rtype: string\n+    :returns: A timezone identifier.\n+    :rtype: string\n \n-        >>> from plone.event.utils import default_timezone\n-        >>> import os\n-        >>> import time\n-        >>> timetz = time.tzname\n-        >>> ostz = \'TZ\' in os.environ.keys() and os.environ[\'TZ\'] or None\n+    >>> from plone.event.utils import default_timezone\n+    >>> import os\n+    >>> import time\n+    >>> timetz = time.tzname\n+    >>> ostz = \'TZ\' in os.environ.keys() and os.environ[\'TZ\'] or None\n \n-        >>> os.environ[\'TZ\'] = "Europe/Vienna"\n-        >>> default_timezone()\n-        \'Europe/Vienna\'\n+    >>> os.environ[\'TZ\'] = "Europe/Vienna"\n+    >>> default_timezone()\n+    \'Europe/Vienna\'\n \n-        Timezone from time module\n-        >>> os.environ[\'TZ\'] = ""\n-        >>> time.tzname = (\'CET\', \'CEST\')\n-        >>> default_timezone()\n-        \'CET\'\n+    Timezone from time module\n+    >>> os.environ[\'TZ\'] = ""\n+    >>> time.tzname = (\'CET\', \'CEST\')\n+    >>> default_timezone()\n+    \'CET\'\n \n-        Invalid timezone\n-        >>> os.environ[\'TZ\'] = "PST"\n-        >>> default_timezone()\n-        \'UTC\'\n+    Invalid timezone\n+    >>> os.environ[\'TZ\'] = "PST"\n+    >>> default_timezone()\n+    \'UTC\'\n \n-        Invalid timezone with defined fallback\n-        >>> os.environ[\'TZ\'] = ""\n-        >>> time.tzname = None\n-        >>> default_timezone(fallback=\'CET\')\n-        \'CET\'\n+    Invalid timezone with defined fallback\n+    >>> os.environ[\'TZ\'] = ""\n+    >>> time.tzname = None\n+    >>> default_timezone(fallback=\'CET\')\n+    \'CET\'\n \n-        Restore the system timezone\n-        >>> time.tzname = timetz\n-        >>> if ostz:\n-        ...     os.environ[\'TZ\'] = ostz\n-        ... else:\n-        ...     del os.environ[\'TZ\']\n+    Restore the system timezone\n+    >>> time.tzname = timetz\n+    >>> if ostz:\n+    ...     os.environ[\'TZ\'] = ostz\n+    ... else:\n+    ...     del os.environ[\'TZ\']\n \n     """\n \n     timezone = None\n-    if \'TZ\' in os.environ.keys():\n+    if "TZ" in os.environ.keys():\n         # Timezone from OS env var\n-        timezone = os.environ[\'TZ\']\n+        timezone = os.environ["TZ"]\n     if not timezone:\n         # Timezone from python time\n         zones = time.tzname\n@@ -131,15 +131,14 @@ def default_timezone(fallback=\'UTC\'):\n         else:\n             # Default fallback = UTC\n             logger.warn(\n-                \'Operating system\\\'s timezone cannot be found. \'\n-                \'Falling back to UTC.\'\n+                "Operating system\'s timezone cannot be found. " "Falling back to UTC."\n             )\n     return validated_timezone(timezone, fallback)\n \n \n # Display helpers\n def is_same_time(start, end, exact=False):\n-    """ Test if event starts and ends at same time.\n+    """Test if event starts and ends at same time.\n \n     :param start: The start datetime.\n     :type start: Python datetime or Zope DateTime\n@@ -177,13 +176,15 @@ def is_same_time(start, end, exact=False):\n     if exact:\n         return start == end\n     else:\n-        return start.hour == end.hour and\\\n-            start.minute == end.minute and\\\n-            start.second == end.second\n+        return (\n+            start.hour == end.hour\n+            and start.minute == end.minute\n+            and start.second == end.second\n+        )\n \n \n def is_same_day(start, end):\n-    """ Test if event starts and ends at same day.\n+    """Test if event starts and ends at same day.\n \n     >>> from plone.event.utils import is_same_day, utc\n     >>> from datetime import datetime, timedelta\n@@ -218,18 +219,18 @@ def is_same_day(start, end):\n \n # Timezone helpers\n def utctz():\n-    """ Return the UTVC zone as a pytz.UTC instance.\n+    """Return the UTVC zone as a pytz.UTC instance.\n \n     >>> from plone.event.utils import utctz\n     >>> utctz()\n     <UTC>\n \n     """\n-    return pytz.timezone(\'UTC\')\n+    return pytz.timezone("UTC")\n \n \n def utc(dt):\n-    """ Convert Python datetime to UTC.\n+    """Convert Python datetime to UTC.\n \n     >>> from datetime import datetime\n     >>> from plone.event.utils import utc\n@@ -250,6 +251,8 @@ def utc(dt):\n     if dt is None:\n         return None\n     dt = pydt(dt)\n+    if dt is None:\n+        return None\n     return dt.astimezone(utctz())\n \n \n@@ -275,12 +278,12 @@ def utcoffset_normalize(date, delta=None, dstmode=DSTAUTO):\n                   used - otherwise DSTADJUST. This behavior is the default.\n     """\n     try:\n-        assert (bool(date.tzinfo))\n+        assert bool(date.tzinfo)\n     except Exception:\n-        raise TypeError(\'Cannot normalize timezone naive dates\')\n-    assert (dstmode in [DSTADJUST, DSTKEEP, DSTAUTO])\n+        raise TypeError("Cannot normalize timezone naive dates")\n+    assert dstmode in [DSTADJUST, DSTKEEP, DSTAUTO]\n     if delta:\n-        assert (isinstance(delta, timedelta))  # Easier in Java\n+        assert isinstance(delta, timedelta)  # Easier in Java\n         delta = delta.seconds + delta.days * 24 * 3600  # total delta in secs\n         if dstmode == DSTAUTO and delta < 24 * 60 * 60:\n             dstmode = DSTKEEP\n@@ -301,7 +304,7 @@ def utcoffset_normalize(date, delta=None, dstmode=DSTAUTO):\n \n \n def tzdel(dt):\n-    """ Create timezone naive datetime from a timezone aware one by removing\n+    """Create timezone naive datetime from a timezone aware one by removing\n     the timezone component.\n \n     >>> from plone.event.utils import tzdel, utctz\n@@ -392,7 +395,7 @@ def date_to_datetime(value):\n     elif is_datetime(value):\n         return value\n     else:\n-        raise ValueError(\'Value must be a date or datetime object.\')\n+        raise ValueError("Value must be a date or datetime object.")\n \n \n def pydt(dt, missing_zone=None, exact=False):\n@@ -454,13 +457,13 @@ def pydt(dt, missing_zone=None, exact=False):\n         dt = datetime(dt.year, dt.month, dt.day)\n \n     if isinstance(dt, datetime):\n-        tznaive = not bool(getattr(dt, \'tzinfo\', False))\n+        tznaive = not bool(getattr(dt, "tzinfo", False))\n         if tznaive:\n             ret = missing_zone.localize(dt)\n         else:\n             ret = utcoffset_normalize(dt, dstmode=DSTADJUST)\n \n-    if \'DateTime\' in str(dt.__class__):\n+    if "DateTime" in str(dt.__class__):\n         # Zope DateTime\n         # TODO: do we need to support subclasses of DateTime too? the check\n         #       above would fail.\n@@ -536,7 +539,7 @@ def guesstz(DT):\n \n # Date as integer representation helpers\n def dt2int(dt):\n-    """ Calculates an integer from a datetime, resolution is one minute.\n+    """Calculates an integer from a datetime, resolution is one minute.\n     The datetime is always converted to the UTC zone.\n \n     >>> from plone.event import utils\n@@ -549,21 +552,22 @@ def dt2int(dt):\n         return 0\n     # TODO: if dt has not timezone information, guess and set it\n     dt = utc(dt)\n-    value = (((dt.year * 12 + dt.month) * 31 + dt.day) * 24 + dt.hour\n-             ) * 60 + dt.minute\n+    value = (((dt.year * 12 + dt.month) * 31 + dt.day) * 24 + dt.hour) * 60 + dt.minute\n \n     # TODO: unit test me\n     if value > MAX32:\n         # value must be integer fitting in the 32bit range\n         raise OverflowError(\n             """{0} is not within the range of indexable dates,<<\n-            exceeding 32bit range.""".format(dt)\n+            exceeding 32bit range.""".format(\n+                dt\n+            )\n         )\n     return value\n \n \n def int2dt(dtint):\n-    """ Returns a datetime object from an integer representation with\n+    """Returns a datetime object from an integer representation with\n     resolution of one minute. The datetime returned is in the UTC zone.\n \n     >>> from plone.event.utils import int2dt\n@@ -578,7 +582,7 @@ def int2dt(dtint):\n \n     """\n     if not isinstance(dtint, int):\n-        raise ValueError(\'int2dt expects integer values as arguments.\')\n+        raise ValueError("int2dt expects integer values as arguments.")\n     minutes = dtint % 60\n     hours = dtint // 60 % 24\n     days = dtint // 60 // 24 % 31\n@@ -588,7 +592,7 @@ def int2dt(dtint):\n \n \n def dt_to_zone(dt, tzstring):\n-    """ Return a datetime instance converted to the timezone given by the\n+    """Return a datetime instance converted to the timezone given by the\n     string.\n \n     """\n@@ -596,8 +600,8 @@ def dt_to_zone(dt, tzstring):\n \n \n # RFC2445 export helpers\n-def rfc2445dt(dt, mode=\'utc\', date=True, time=True):\n-    """ Convert a datetime or DateTime object into an RFC2445 compatible\n+def rfc2445dt(dt, mode="utc", date=True, time=True):\n+    """Convert a datetime or DateTime object into an RFC2445 compatible\n     datetime string.\n \n     @param dt: datetime or DateTime object to convert.\n@@ -657,14 +661,14 @@ def rfc2445dt(dt, mode=\'utc\', date=True, time=True):\n     # TODO: rfc2445dt might not be necessary. drop me then.\n \n     dt = pydt(dt)\n-    if mode == \'utc\':\n+    if mode == "utc":\n         dt = utc(dt)\n-    date = \'{0}{1}{2}{3}\'.format(\n-        date and dt.strftime(\'%Y%m%d\') or \'\',\n-        date and time and \'T\' or \'\',\n-        time and dt.strftime(\'%H%M%S\') or \'\',\n-        mode == \'utc\' and \'Z\' or \'\',\n+    date = "{0}{1}{2}{3}".format(\n+        date and dt.strftime("%Y%m%d") or "",\n+        date and time and "T" or "",\n+        time and dt.strftime("%H%M%S") or "",\n+        mode == "utc" and "Z" or "",\n     )\n-    if mode == \'local\':\n+    if mode == "local":\n         return date, dt.tzinfo.zone\n     return date\n'
+
+Repository: plone.event
+
+
+Branch: refs/heads/master
+Date: 2023-01-13T12:10:01+01:00
+Author: Jens W. Klein (jensens) <jk@kleinundpartner.at>
+Commit: https://github.com/plone/plone.event/commit/a6a0923a657d376df74d15ad8099e961c3bb18b6
+
+Merge pull request #15 from plone/issue-#13
+
+Fixing #13
+
+Files changed:
+A news/13.bugfix
+M plone/event/utils.py
+
+b'diff --git a/news/13.bugfix b/news/13.bugfix\nnew file mode 100644\nindex 0000000..5bbd512\n--- /dev/null\n+++ b/news/13.bugfix\n@@ -0,0 +1 @@\n+Fixing issue #13\n\\ No newline at end of file\ndiff --git a/plone/event/utils.py b/plone/event/utils.py\nindex e7681f8..0763205 100644\n--- a/plone/event/utils.py\n+++ b/plone/event/utils.py\n@@ -9,16 +9,16 @@\n import time\n \n \n-DSTADJUST = \'adjust\'\n-DSTKEEP = \'keep\'\n-DSTAUTO = \'auto\'\n+DSTADJUST = "adjust"\n+DSTKEEP = "keep"\n+DSTAUTO = "auto"\n MAX32 = int(2**31 - 1)\n \n-logger = logging.getLogger(\'plone.event\')\n+logger = logging.getLogger("plone.event")\n \n \n def validated_timezone(timezone, fallback=None):\n-    """ Validate a given timezone identifier. If a fallback is given, return it\n+    """Validate a given timezone identifier. If a fallback is given, return it\n         when the given timezone is not a valid pytz zone. Else raise an\n         ValueError exception.\n \n@@ -59,8 +59,8 @@ def validated_timezone(timezone, fallback=None):\n     except Exception:\n         if fallback:\n             logger.warn(\n-                \'The timezone {0} is not a valid timezone from the \'\n-                \'Olson database or pytz. Falling back to {1}.\'.format(\n+                "The timezone {0} is not a valid timezone from the "\n+                "Olson database or pytz. Falling back to {1}.".format(\n                     timezone,\n                     fallback,\n                 )\n@@ -68,61 +68,61 @@ def validated_timezone(timezone, fallback=None):\n             return fallback\n         else:\n             raise ValueError(\n-                \'The timezone {0} is not a valid timezone from \'\n-                \'the Olson database or pytz.\'.format(timezone)\n+                "The timezone {0} is not a valid timezone from "\n+                "the Olson database or pytz.".format(timezone)\n             )\n \n \n-def default_timezone(fallback=\'UTC\'):\n-    """ Retrieve the timezone from the server.\n-        Default Fallback: UTC\n+def default_timezone(fallback="UTC"):\n+    """Retrieve the timezone from the server.\n+    Default Fallback: UTC\n \n-        :param fallback: A fallback timezone identifier.\n-        :type fallback: string\n+    :param fallback: A fallback timezone identifier.\n+    :type fallback: string\n \n-        :returns: A timezone identifier.\n-        :rtype: string\n+    :returns: A timezone identifier.\n+    :rtype: string\n \n-        >>> from plone.event.utils import default_timezone\n-        >>> import os\n-        >>> import time\n-        >>> timetz = time.tzname\n-        >>> ostz = \'TZ\' in os.environ.keys() and os.environ[\'TZ\'] or None\n+    >>> from plone.event.utils import default_timezone\n+    >>> import os\n+    >>> import time\n+    >>> timetz = time.tzname\n+    >>> ostz = \'TZ\' in os.environ.keys() and os.environ[\'TZ\'] or None\n \n-        >>> os.environ[\'TZ\'] = "Europe/Vienna"\n-        >>> default_timezone()\n-        \'Europe/Vienna\'\n+    >>> os.environ[\'TZ\'] = "Europe/Vienna"\n+    >>> default_timezone()\n+    \'Europe/Vienna\'\n \n-        Timezone from time module\n-        >>> os.environ[\'TZ\'] = ""\n-        >>> time.tzname = (\'CET\', \'CEST\')\n-        >>> default_timezone()\n-        \'CET\'\n+    Timezone from time module\n+    >>> os.environ[\'TZ\'] = ""\n+    >>> time.tzname = (\'CET\', \'CEST\')\n+    >>> default_timezone()\n+    \'CET\'\n \n-        Invalid timezone\n-        >>> os.environ[\'TZ\'] = "PST"\n-        >>> default_timezone()\n-        \'UTC\'\n+    Invalid timezone\n+    >>> os.environ[\'TZ\'] = "PST"\n+    >>> default_timezone()\n+    \'UTC\'\n \n-        Invalid timezone with defined fallback\n-        >>> os.environ[\'TZ\'] = ""\n-        >>> time.tzname = None\n-        >>> default_timezone(fallback=\'CET\')\n-        \'CET\'\n+    Invalid timezone with defined fallback\n+    >>> os.environ[\'TZ\'] = ""\n+    >>> time.tzname = None\n+    >>> default_timezone(fallback=\'CET\')\n+    \'CET\'\n \n-        Restore the system timezone\n-        >>> time.tzname = timetz\n-        >>> if ostz:\n-        ...     os.environ[\'TZ\'] = ostz\n-        ... else:\n-        ...     del os.environ[\'TZ\']\n+    Restore the system timezone\n+    >>> time.tzname = timetz\n+    >>> if ostz:\n+    ...     os.environ[\'TZ\'] = ostz\n+    ... else:\n+    ...     del os.environ[\'TZ\']\n \n     """\n \n     timezone = None\n-    if \'TZ\' in os.environ.keys():\n+    if "TZ" in os.environ.keys():\n         # Timezone from OS env var\n-        timezone = os.environ[\'TZ\']\n+        timezone = os.environ["TZ"]\n     if not timezone:\n         # Timezone from python time\n         zones = time.tzname\n@@ -131,15 +131,14 @@ def default_timezone(fallback=\'UTC\'):\n         else:\n             # Default fallback = UTC\n             logger.warn(\n-                \'Operating system\\\'s timezone cannot be found. \'\n-                \'Falling back to UTC.\'\n+                "Operating system\'s timezone cannot be found. " "Falling back to UTC."\n             )\n     return validated_timezone(timezone, fallback)\n \n \n # Display helpers\n def is_same_time(start, end, exact=False):\n-    """ Test if event starts and ends at same time.\n+    """Test if event starts and ends at same time.\n \n     :param start: The start datetime.\n     :type start: Python datetime or Zope DateTime\n@@ -177,13 +176,15 @@ def is_same_time(start, end, exact=False):\n     if exact:\n         return start == end\n     else:\n-        return start.hour == end.hour and\\\n-            start.minute == end.minute and\\\n-            start.second == end.second\n+        return (\n+            start.hour == end.hour\n+            and start.minute == end.minute\n+            and start.second == end.second\n+        )\n \n \n def is_same_day(start, end):\n-    """ Test if event starts and ends at same day.\n+    """Test if event starts and ends at same day.\n \n     >>> from plone.event.utils import is_same_day, utc\n     >>> from datetime import datetime, timedelta\n@@ -218,18 +219,18 @@ def is_same_day(start, end):\n \n # Timezone helpers\n def utctz():\n-    """ Return the UTVC zone as a pytz.UTC instance.\n+    """Return the UTVC zone as a pytz.UTC instance.\n \n     >>> from plone.event.utils import utctz\n     >>> utctz()\n     <UTC>\n \n     """\n-    return pytz.timezone(\'UTC\')\n+    return pytz.timezone("UTC")\n \n \n def utc(dt):\n-    """ Convert Python datetime to UTC.\n+    """Convert Python datetime to UTC.\n \n     >>> from datetime import datetime\n     >>> from plone.event.utils import utc\n@@ -250,6 +251,8 @@ def utc(dt):\n     if dt is None:\n         return None\n     dt = pydt(dt)\n+    if dt is None:\n+        return None\n     return dt.astimezone(utctz())\n \n \n@@ -275,12 +278,12 @@ def utcoffset_normalize(date, delta=None, dstmode=DSTAUTO):\n                   used - otherwise DSTADJUST. This behavior is the default.\n     """\n     try:\n-        assert (bool(date.tzinfo))\n+        assert bool(date.tzinfo)\n     except Exception:\n-        raise TypeError(\'Cannot normalize timezone naive dates\')\n-    assert (dstmode in [DSTADJUST, DSTKEEP, DSTAUTO])\n+        raise TypeError("Cannot normalize timezone naive dates")\n+    assert dstmode in [DSTADJUST, DSTKEEP, DSTAUTO]\n     if delta:\n-        assert (isinstance(delta, timedelta))  # Easier in Java\n+        assert isinstance(delta, timedelta)  # Easier in Java\n         delta = delta.seconds + delta.days * 24 * 3600  # total delta in secs\n         if dstmode == DSTAUTO and delta < 24 * 60 * 60:\n             dstmode = DSTKEEP\n@@ -301,7 +304,7 @@ def utcoffset_normalize(date, delta=None, dstmode=DSTAUTO):\n \n \n def tzdel(dt):\n-    """ Create timezone naive datetime from a timezone aware one by removing\n+    """Create timezone naive datetime from a timezone aware one by removing\n     the timezone component.\n \n     >>> from plone.event.utils import tzdel, utctz\n@@ -392,7 +395,7 @@ def date_to_datetime(value):\n     elif is_datetime(value):\n         return value\n     else:\n-        raise ValueError(\'Value must be a date or datetime object.\')\n+        raise ValueError("Value must be a date or datetime object.")\n \n \n def pydt(dt, missing_zone=None, exact=False):\n@@ -454,13 +457,13 @@ def pydt(dt, missing_zone=None, exact=False):\n         dt = datetime(dt.year, dt.month, dt.day)\n \n     if isinstance(dt, datetime):\n-        tznaive = not bool(getattr(dt, \'tzinfo\', False))\n+        tznaive = not bool(getattr(dt, "tzinfo", False))\n         if tznaive:\n             ret = missing_zone.localize(dt)\n         else:\n             ret = utcoffset_normalize(dt, dstmode=DSTADJUST)\n \n-    if \'DateTime\' in str(dt.__class__):\n+    if "DateTime" in str(dt.__class__):\n         # Zope DateTime\n         # TODO: do we need to support subclasses of DateTime too? the check\n         #       above would fail.\n@@ -536,7 +539,7 @@ def guesstz(DT):\n \n # Date as integer representation helpers\n def dt2int(dt):\n-    """ Calculates an integer from a datetime, resolution is one minute.\n+    """Calculates an integer from a datetime, resolution is one minute.\n     The datetime is always converted to the UTC zone.\n \n     >>> from plone.event import utils\n@@ -549,21 +552,22 @@ def dt2int(dt):\n         return 0\n     # TODO: if dt has not timezone information, guess and set it\n     dt = utc(dt)\n-    value = (((dt.year * 12 + dt.month) * 31 + dt.day) * 24 + dt.hour\n-             ) * 60 + dt.minute\n+    value = (((dt.year * 12 + dt.month) * 31 + dt.day) * 24 + dt.hour) * 60 + dt.minute\n \n     # TODO: unit test me\n     if value > MAX32:\n         # value must be integer fitting in the 32bit range\n         raise OverflowError(\n             """{0} is not within the range of indexable dates,<<\n-            exceeding 32bit range.""".format(dt)\n+            exceeding 32bit range.""".format(\n+                dt\n+            )\n         )\n     return value\n \n \n def int2dt(dtint):\n-    """ Returns a datetime object from an integer representation with\n+    """Returns a datetime object from an integer representation with\n     resolution of one minute. The datetime returned is in the UTC zone.\n \n     >>> from plone.event.utils import int2dt\n@@ -578,7 +582,7 @@ def int2dt(dtint):\n \n     """\n     if not isinstance(dtint, int):\n-        raise ValueError(\'int2dt expects integer values as arguments.\')\n+        raise ValueError("int2dt expects integer values as arguments.")\n     minutes = dtint % 60\n     hours = dtint // 60 % 24\n     days = dtint // 60 // 24 % 31\n@@ -588,7 +592,7 @@ def int2dt(dtint):\n \n \n def dt_to_zone(dt, tzstring):\n-    """ Return a datetime instance converted to the timezone given by the\n+    """Return a datetime instance converted to the timezone given by the\n     string.\n \n     """\n@@ -596,8 +600,8 @@ def dt_to_zone(dt, tzstring):\n \n \n # RFC2445 export helpers\n-def rfc2445dt(dt, mode=\'utc\', date=True, time=True):\n-    """ Convert a datetime or DateTime object into an RFC2445 compatible\n+def rfc2445dt(dt, mode="utc", date=True, time=True):\n+    """Convert a datetime or DateTime object into an RFC2445 compatible\n     datetime string.\n \n     @param dt: datetime or DateTime object to convert.\n@@ -657,14 +661,14 @@ def rfc2445dt(dt, mode=\'utc\', date=True, time=True):\n     # TODO: rfc2445dt might not be necessary. drop me then.\n \n     dt = pydt(dt)\n-    if mode == \'utc\':\n+    if mode == "utc":\n         dt = utc(dt)\n-    date = \'{0}{1}{2}{3}\'.format(\n-        date and dt.strftime(\'%Y%m%d\') or \'\',\n-        date and time and \'T\' or \'\',\n-        time and dt.strftime(\'%H%M%S\') or \'\',\n-        mode == \'utc\' and \'Z\' or \'\',\n+    date = "{0}{1}{2}{3}".format(\n+        date and dt.strftime("%Y%m%d") or "",\n+        date and time and "T" or "",\n+        time and dt.strftime("%H%M%S") or "",\n+        mode == "utc" and "Z" or "",\n     )\n-    if mode == \'local\':\n+    if mode == "local":\n         return date, dt.tzinfo.zone\n     return date\n'