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@@ -154,7 +154,7 @@
 
 fobj: io.IOBase
 
-def __init__(self, fileish: str | io.IOBase, *args, compression: str | None, **kwargs):
+def __init__(self, fileish: str | io.IOBase, *args, compression: str | None = None, **kwargs):
 if isinstance(fileish, (io.IOBase, Fileish)):
 self.fobj = fileish
 self.me_opened = False
@@ -187,8 +187,8 @@
 def _get_opener_argnames(self, fileish: str, compression: str | None) -> OpenerDef:
 if compression is not None:
 if compression[0] != '.':
 compression = f'.{compression}'
 return self.compress_ext_map[compression]
 _, ext = splitext(fileish)
 if self.compress_ext_icase:
 ext = ext.lower()