--- a/Lib/_pyio.py
+++ b/Lib/_pyio.py
@@ -556,7 +556,11 @@ class RawIOBase(IOBase):
             if not data:
                 break
             res += data
-        return bytes(res)
+        if res:
+            return bytes(res)
+        else:
+            # b'' or None
+            return data
 
     def readinto(self, b):
         """Read up to len(b) bytes into b.

--- a/Lib/test/test_io.py
+++ b/Lib/test/test_io.py
@@ -790,14 +790,17 @@ class BufferedReaderTest(unittest.TestCa
         # Inject some None's in there to simulate EWOULDBLOCK
         rawio = self.MockRawIO((b"abc", b"d", None, b"efg", None, None, None))
         bufio = self.tp(rawio)
-
         self.assertEqual(b"abcd", bufio.read(6))
         self.assertEqual(b"e", bufio.read(1))
         self.assertEqual(b"fg", bufio.read())
         self.assertEqual(b"", bufio.peek(1))
-        self.assertTrue(None is bufio.read())
+        self.assertIsNone(bufio.read())
         self.assertEqual(b"", bufio.read())
 
+        rawio = self.MockRawIO((b"a", None, None))
+        self.assertEqual(b"a", rawio.readall())
+        self.assertIsNone(rawio.readall())
+
     def test_read_past_eof(self):
         rawio = self.MockRawIO((b"abc", b"d", b"efg"))
         bufio = self.tp(rawio)

--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -75,6 +75,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #12175: RawIOBase.readall() now returns None if read() returns None.
+
 - Issue #12175: FileIO.readall() now raises a ValueError instead of an IOError
   if the file is closed.
 

--- a/Modules/_io/iobase.c
+++ b/Modules/_io/iobase.c
@@ -814,6 +814,14 @@ rawiobase_readall(PyObject *self, PyObje
             Py_DECREF(chunks);
             return NULL;
         }
+        if (data == Py_None) {
+            if (PyList_GET_SIZE(chunks) == 0) {
+                Py_DECREF(chunks);
+                return data;
+            }
+            Py_DECREF(data);
+            break;
+        }
         if (!PyBytes_Check(data)) {
             Py_DECREF(chunks);
             Py_DECREF(data);