diff --git a/docs/portal.md b/docs/portal.md
index f3a22a3e..468af179 100644
--- a/docs/portal.md
+++ b/docs/portal.md
@@ -205,12 +205,7 @@ api.portal.send_email(
 %
 % self.assertEqual(len(mailhost.messages), 1)
 %
-% try:
-%     # Python 3
-%     from email import message_from_bytes
-% except ImportError:
-%     # Python 2
-%     from email import message_from_string as message_from_bytes
+% from email import message_from_bytes
 % msg = message_from_bytes(mailhost.messages[0])
 % self.assertEqual(msg['To'], 'bob@plone.org')
 % self.assertEqual(msg['From'], 'noreply@plone.org')
diff --git a/news/592.bugfix.md b/news/592.bugfix.md
new file mode 100644
index 00000000..b55dbc5e
--- /dev/null
+++ b/news/592.bugfix.md
@@ -0,0 +1 @@
+Clean up. @ale-rt
diff --git a/src/plone/api/content.py b/src/plone/api/content.py
index 9d4c6d91..552afffd 100644
--- a/src/plone/api/content.py
+++ b/src/plone/api/content.py
@@ -25,7 +25,7 @@
 import transaction
 import uuid
 
-_marker = []
+_marker = object()
 
 # Maximum number of attempts to generate a unique random ID
 MAX_UNIQUE_ID_ATTEMPTS = 100
@@ -753,7 +753,7 @@ def iter_ancestors(obj=None, function=None, interface=None, stop_at=_marker):
         #
         # This is useful if we want to have an empty iterator when checking
         # for ancestors in the portal.
-        return iter(())
+        yield from ()
 
     chain = aq_chain(aq_inner(obj))
 
diff --git a/src/plone/api/portal.py b/src/plone/api/portal.py
index 6d3f1b46..74e8bf98 100644
--- a/src/plone/api/portal.py
+++ b/src/plone/api/portal.py
@@ -170,11 +170,6 @@ def send_email(
             # formataddr probably got confused by special characters.
             sender = from_address
 
-    # If the mail headers are not properly encoded we need to extract
-    # them and let MailHost manage the encoding.
-    if isinstance(body, str):
-        body = body.encode(encoding)
-
     host = get_tool("MailHost")
     host.send(
         body,
diff --git a/src/plone/api/tests/test_portal.py b/src/plone/api/tests/test_portal.py
index ac8124d7..e5bb0076 100644
--- a/src/plone/api/tests/test_portal.py
+++ b/src/plone/api/tests/test_portal.py
@@ -2,6 +2,7 @@
 
 from datetime import date
 from datetime import datetime
+from email import message_from_bytes
 from packaging import version
 from plone.api import content
 from plone.api import env
@@ -25,14 +26,6 @@
 import DateTime
 import unittest
 
-try:
-    # Python 3
-    from email import message_from_bytes
-except ImportError:
-    # Python 2
-    from email import message_from_string as message_from_bytes
-
-
 HAS_PLONE5 = version.parse(env.plone_version()) >= version.parse("5.0b2")
 
 
diff --git a/src/plone/api/user.py b/src/plone/api/user.py
index 2e93b98f..a82de89c 100644
--- a/src/plone/api/user.py
+++ b/src/plone/api/user.py
@@ -438,9 +438,16 @@ def revoke_roles(username=None, user=None, obj=None, roles=None):
     if user is None:
         raise InvalidParameterError("User could not be found")
 
-    roles = set(roles)
-
-    if "Anonymous" in roles or "Authenticated" in roles:
+    try:
+        roles_set = set(roles)
+        if not all(isinstance(role, str) for role in roles_set):
+            raise InvalidParameterError(
+                "Roles must be an iterable containing only strings"
+            )
+    except TypeError:
+        raise InvalidParameterError("Roles must be an iterable containing only strings")
+
+    if "Anonymous" in roles_set or "Authenticated" in roles_set:
         raise InvalidParameterError
 
     inherit = True
@@ -454,7 +461,7 @@ def revoke_roles(username=None, user=None, obj=None, roles=None):
         if role not in ["Anonymous", "Authenticated"]
     }
 
-    roles = list(actual_roles - roles)
+    roles = list(actual_roles - roles_set)
 
     if obj is None:
         user.setSecurityProfile(roles=roles)