IRCBuffer.find's not_pattern arg should be optional

Author: jesopo

src/IRCBuffer.py

@@ -56,7 +56,7 @@ def get_all(self, for_user: typing.Optional[str]=None):
                 yield line
 
     def find(self, pattern: typing.Union[str, typing.Pattern[str]],
-            not_pattern: typing.Union[str, typing.Pattern[str]],
+            not_pattern: typing.Union[str, typing.Pattern[str]]=None,
             from_self=True, for_user: str=None, deleted=False
             ) -> typing.Optional[BufferLineMatch]:
         if for_user: