diff --git a/libp2p/__init__.py b/libp2p/__init__.py
index 9e452ca..08caf25 100644
--- a/libp2p/__init__.py
+++ b/libp2p/__init__.py
@@ -1,5 +1,5 @@
 import asyncio
-from typing import Mapping, Sequence
+from typing import Sequence
 
 from libp2p.crypto.keys import KeyPair
 from libp2p.crypto.rsa import create_new_key_pair
@@ -15,10 +15,9 @@ from libp2p.routing.interfaces import IPeerRouting
 from libp2p.routing.kademlia.kademlia_peer_router import KadmeliaPeerRouter
 from libp2p.security.insecure.transport import PLAINTEXT_PROTOCOL_ID, InsecureTransport
 import libp2p.security.secio.transport as secio
-from libp2p.security.secure_transport_interface import ISecureTransport
 from libp2p.stream_muxer.mplex.mplex import MPLEX_PROTOCOL_ID, Mplex
 from libp2p.transport.tcp.tcp import TCP
-from libp2p.transport.typing import TMuxerClass, TMuxerOptions, TSecurityOptions
+from libp2p.transport.typing import TMuxerOptions, TSecurityOptions
 from libp2p.transport.upgrader import TransportUpgrader
 from libp2p.typing import TProtocol
 
diff --git a/libp2p/security/security_multistream.py b/libp2p/security/security_multistream.py
index 06f4b8a..cff55af 100644
--- a/libp2p/security/security_multistream.py
+++ b/libp2p/security/security_multistream.py
@@ -31,14 +31,13 @@ class SecurityMultistream(ABC):
     multiselect: Multiselect
     multiselect_client: MultiselectClient
 
-    def __init__(self, secure_transports_by_protocol: TSecurityOptions = None) -> None:
+    def __init__(self, secure_transports_by_protocol: TSecurityOptions) -> None:
         self.transports = OrderedDict()
         self.multiselect = Multiselect()
         self.multiselect_client = MultiselectClient()
 
-        if secure_transports_by_protocol is not None:
-            for protocol, transport in secure_transports_by_protocol.items():
-                self.add_transport(protocol, transport)
+        for protocol, transport in secure_transports_by_protocol.items():
+            self.add_transport(protocol, transport)
 
     def add_transport(self, protocol: TProtocol, transport: ISecureTransport) -> None:
         """
diff --git a/libp2p/stream_muxer/muxer_multistream.py b/libp2p/stream_muxer/muxer_multistream.py
index d506749..7f6ee07 100644
--- a/libp2p/stream_muxer/muxer_multistream.py
+++ b/libp2p/stream_muxer/muxer_multistream.py
@@ -26,13 +26,12 @@ class MuxerMultistream:
     multiselect: Multiselect
     multiselect_client: MultiselectClient
 
-    def __init__(self, muxer_transports_by_protocol: TMuxerOptions = None) -> None:
+    def __init__(self, muxer_transports_by_protocol: TMuxerOptions) -> None:
         self.transports = OrderedDict()
         self.multiselect = Multiselect()
         self.multiselect_client = MultiselectClient()
-        if muxer_transports_by_protocol is not None:
-            for protocol, transport in muxer_transports_by_protocol.items():
-                self.add_transport(protocol, transport)
+        for protocol, transport in muxer_transports_by_protocol.items():
+            self.add_transport(protocol, transport)
 
     def add_transport(self, protocol: TProtocol, transport: TMuxerClass) -> None:
         """