use "Optional" in typing

csdr/chain/__init__.py

@@ -1,7 +1,7 @@
 from csdr.module import Module
 from pycsdr.modules import Buffer
 from pycsdr.types import Format
-from typing import Union, Callable
+from typing import Union, Callable, Optional
 
 
 class Chain(Module):
@@ -15,7 +15,7 @@ class Chain(Module):
     def empty(self):
         return not self.workers
 
-    def _connect(self, w1, w2, buffer: Union[Buffer, None] = None) -> None:
+    def _connect(self, w1, w2, buffer: Optional[Buffer] = None) -> None:
         if buffer is None:
             buffer = Buffer(w1.getOutputFormat())
         w1.setWriter(buffer)

owrx/dsp.py

@@ -9,7 +9,7 @@ from csdr.chain.clientaudio import ClientAudioChain
 from csdr.chain.fft import FftChain
 from pycsdr.modules import Buffer, Writer
 from pycsdr.types import Format
-from typing import Union
+from typing import Union, Optional
 from io import BytesIO
 import threading
 import re
@@ -52,7 +52,7 @@ class ClientDemodulatorChain(Chain):
             self.secondaryDemodulator.stop()
             self.secondaryDemodulator = None
 
-    def _connect(self, w1, w2, buffer: Union[Buffer, None] = None) -> None:
+    def _connect(self, w1, w2, buffer: Optional[Buffer] = None) -> None:
         if w1 is self.selector:
             super()._connect(w1, w2, self.selectorBuffer)
         elif w2 is self.clientAudioChain:
@@ -115,7 +115,7 @@ class ClientDemodulatorChain(Chain):
             return self.secondaryDemodulator.getFixedAudioRate()
         return self.outputRate
 
-    def setSecondaryDemodulator(self, demod: Union[SecondaryDemodulator, None]):
+    def setSecondaryDemodulator(self, demod: Optional[SecondaryDemodulator]):
         if demod is self.secondaryDemodulator:
             return