diff --git a/keyring/backends/Windows.py b/keyring/backends/Windows.py
index 110075b2..f0537c2e 100644
--- a/keyring/backends/Windows.py
+++ b/keyring/backends/Windows.py
@@ -92,7 +92,7 @@ def priority(cls) -> float:
         return 5
 
     @staticmethod
-    def _compound_name(username, service):
+    def _compound_name(username: str | None, service: str) -> str:
         return f'{username}@{service}'
 
     def get_password(self, service, username):
diff --git a/keyring/backends/chainer.py b/keyring/backends/chainer.py
index 6bc711f1..48d238f3 100644
--- a/keyring/backends/chainer.py
+++ b/keyring/backends/chainer.py
@@ -3,7 +3,7 @@
 discover passwords in each.
 """
 
-from .. import backend
+from .. import backend, credentials
 from ..compat import properties
 from . import fail
 
@@ -28,12 +28,12 @@ def priority(cls) -> float:
         return 10 if len(cls.backends) > 1 else (fail.Keyring.priority - 1)
 
     @properties.classproperty
-    def backends(cls):
+    def backends(cls) -> list[backend.KeyringBackend]:
         """
         Discover all keyrings for chaining.
         """
 
-        def allow(keyring):
+        def allow(keyring: backend.KeyringBackend) -> bool:
             limit = backend._limit or bool
             return (
                 not isinstance(keyring, ChainerBackend)
@@ -44,28 +44,34 @@ def allow(keyring):
         allowed = filter(allow, backend.get_all_keyring())
         return sorted(allowed, key=backend.by_priority, reverse=True)
 
-    def get_password(self, service, username):
+    def get_password(self, service: str, username: str) -> str | None:
         for keyring in self.backends:
             password = keyring.get_password(service, username)
             if password is not None:
                 return password
+        return None
 
-    def set_password(self, service, username, password):
+    def set_password(self, service: str, username: str, password: str) -> None:
         for keyring in self.backends:
             try:
                 return keyring.set_password(service, username, password)
             except NotImplementedError:
                 pass
 
-    def delete_password(self, service, username):
+    def delete_password(self, service: str, username: str) -> None:
         for keyring in self.backends:
             try:
                 return keyring.delete_password(service, username)
             except NotImplementedError:
                 pass
 
-    def get_credential(self, service, username):
+    def get_credential(
+        self,
+        service: str,
+        username: str | None,
+    ) -> credentials.Credential | None:
         for keyring in self.backends:
             credential = keyring.get_credential(service, username)
             if credential is not None:
                 return credential
+        return None
diff --git a/keyring/testing/backend.py b/keyring/testing/backend.py
index 89a414bf..f1b36223 100644
--- a/keyring/testing/backend.py
+++ b/keyring/testing/backend.py
@@ -25,7 +25,7 @@
 assert min(ord(char) for char in UNICODE_CHARS) > 127
 
 
-def is_ascii_printable(s):
+def is_ascii_printable(s: str) -> bool:
     return all(32 <= ord(c) < 127 for c in s)
 
 
@@ -44,13 +44,13 @@ def cleanup(self):
         for item in self.credentials_created:
             self.keyring.delete_password(*item)
 
-    def set_password(self, service, username, password):
+    def set_password(self, service: str, username: str, password: str) -> None:
         # set the password and save the result so the test runner can clean
         #  up after if necessary.
         self.keyring.set_password(service, username, password)
         self.credentials_created.add((service, username))
 
-    def check_set_get(self, service, username, password):
+    def check_set_get(self, service: str, username: str, password: str) -> None:
         keyring = self.keyring
 
         # for the non-existent password
diff --git a/keyring/testing/util.py b/keyring/testing/util.py
index b8ef4c68..0bfc0bb0 100644
--- a/keyring/testing/util.py
+++ b/keyring/testing/util.py
@@ -63,6 +63,6 @@ def Environ(**changes):
 ALPHABET = string.ascii_letters + string.digits
 
 
-def random_string(k, source=ALPHABET):
+def random_string(k: int, source: str=ALPHABET) -> str:
     """Generate a random string with length <i>k</i>"""
     return ''.join(random.choice(source) for _unused in range(k))