doc: make unshift doc compliant with push doc

readable.unshift() also allows to pass null and end stream

readable.push() don't allow null when in object mode

doc/api/stream.md

@@ -1244,13 +1244,15 @@ changes:
     description: The `chunk` argument can now be a `Uint8Array` instance.
 -->
 
-* `chunk` {Buffer|Uint8Array|string|any} Chunk of data to unshift onto the
+* `chunk` {Buffer|Uint8Array|string|null|any} Chunk of data to unshift onto the
   read queue. For streams not operating in object mode, `chunk` must be a
   string, `Buffer` or `Uint8Array`. For object mode streams, `chunk` may be
   any JavaScript value other than `null`.
 * `encoding` {string} Encoding of string chunks. Must be a valid
   `Buffer` encoding, such as `'utf8'` or `'ascii'`.
 
+Passing chunk as null signals the end of the stream (EOF), after which no more data can be written.
+
 The `readable.unshift()` method pushes a chunk of data back into the internal
 buffer. This is useful in certain situations where a stream is being consumed by
 code that needs to "un-consume" some amount of data that it has optimistically
@@ -2028,7 +2030,7 @@ changes:
 * `chunk` {Buffer|Uint8Array|string|null|any} Chunk of data to push into the
   read queue. For streams not operating in object mode, `chunk` must be a
   string, `Buffer` or `Uint8Array`. For object mode streams, `chunk` may be
-  any JavaScript value.
+  any JavaScript value other than `null`..
 * `encoding` {string} Encoding of string chunks. Must be a valid
   `Buffer` encoding, such as `'utf8'` or `'ascii'`.
 * Returns: {boolean} `true` if additional chunks of data may continue to be