diff --git a/pyproject.toml b/pyproject.toml
index e3b92d0dc1..92b1b7e275 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -24,6 +24,11 @@ disallow_untyped_calls = false
 disallow_untyped_decorators = false
 warn_return_any = false
 
+# Enable optional errors.
+enable_error_code = [
+    "redundant-expr",
+]
+
 # Display the codes needed for # type: ignore[code] annotations.
 show_error_codes = true
 
diff --git a/tools/lib/capitalization.py b/tools/lib/capitalization.py
index 2510b5b2ec..4eee7407e9 100644
--- a/tools/lib/capitalization.py
+++ b/tools/lib/capitalization.py
@@ -218,7 +218,7 @@ def check_capitalization(strings: List[str]) -> Tuple[List[str], List[str], List
         capitalized = is_capitalized(safe_text)
         if not capitalized:
             errors.append(text)
-        elif capitalized and has_ignored_phrase:
+        elif has_ignored_phrase:
             ignored.append(text)
 
         banned_word_errors.extend(check_banned_words(text))
diff --git a/tools/lib/template_parser.py b/tools/lib/template_parser.py
index a015e445fb..76655aa33b 100644
--- a/tools/lib/template_parser.py
+++ b/tools/lib/template_parser.py
@@ -464,7 +464,7 @@ def validate(fn: Optional[str] = None, text: Optional[str] = None) -> List[Token
                         f"Tag must be self-closing: {tag} at {fn} line {token.line}, col {token.col}"
                     )
             elif kind == "html_singleton":
-                if not state.foreign and tag not in HTML_VOID_TAGS:
+                if tag not in HTML_VOID_TAGS:
                     raise TemplateParserException(
                         f"Tag must not be self-closing: {tag} at {fn} line {token.line}, col {token.col}"
                     )
diff --git a/zerver/lib/mention.py b/zerver/lib/mention.py
index 232946aa61..7a1bd3d1a1 100644
--- a/zerver/lib/mention.py
+++ b/zerver/lib/mention.py
@@ -87,8 +87,7 @@ class MentionBackend:
             # We expect callers who take advantage of our cache to supply both
             # id and full_name in the user mentions in their messages.
             for user in user_list:
-                if user.id is not None and user.full_name is not None:
-                    self.user_cache[(user.id, user.full_name)] = user
+                self.user_cache[(user.id, user.full_name)] = user
 
             result += user_list
 
diff --git a/zerver/lib/scim.py b/zerver/lib/scim.py
index a3670b4f19..b21125565e 100644
--- a/zerver/lib/scim.py
+++ b/zerver/lib/scim.py
@@ -181,7 +181,7 @@ class ZulipSCIMUser(SCIMUser):
             self._full_name_new_value = new_value
 
     def change_is_active(self, new_value: bool) -> None:
-        if new_value is not None and new_value != self.obj.is_active:
+        if new_value != self.obj.is_active:
             self._is_active_new_value = new_value
 
     def handle_replace(
diff --git a/zerver/lib/webhooks/common.py b/zerver/lib/webhooks/common.py
index fe89839166..4e736c7a87 100644
--- a/zerver/lib/webhooks/common.py
+++ b/zerver/lib/webhooks/common.py
@@ -114,7 +114,7 @@ def check_send_webhook_message(
         # double escape their URLs in a manner that escaped space characters
         # (%20) are never properly decoded. We work around that by making sure
         # that the URL parameters are decoded on our end.
-        if stream is not None and unquote_url_parameters:
+        if unquote_url_parameters:
             stream = unquote(stream)
 
         if user_specified_topic is not None: