gh-100201: Document behavior with a bare yield statement (#100416)

Co-authored-by: C.A.M. Gerlach <[email protected]>

Author: ramvikrams

Doc/reference/expressions.rst

@@ -454,7 +454,9 @@ generator.  That generator then controls the execution of the generator
 function.  The execution starts when one of the generator's methods is called.
 At that time, the execution proceeds to the first yield expression, where it is
 suspended again, returning the value of :token:`~python-grammar:expression_list`
-to the generator's caller.  By suspended, we mean that all local state is
+to the generator's caller,
+or ``None`` if :token:`~python-grammer:expression_list` is omitted.
+By suspended, we mean that all local state is
 retained, including the current bindings of local variables, the instruction
 pointer, the internal evaluation stack, and the state of any exception handling.
 When the execution is resumed by calling one of the generator's methods, the