bpo-31065: Add doc about Popen.poll returning None. (#3169)

diff --git a/Doc/library/subprocess.rst b/Doc/library/subprocess.rst
index 2eaa48e070dcb85aee49606219794818eef92c48..a4e234e62aeca5f9de5d4c3b6e1876c2786971ad 100644 (file)
--- a/Doc/library/subprocess.rst
+++ b/Doc/library/subprocess.rst
@@ -584,7 +584,7 @@ Instances of the :class:`Popen` class have the following methods:
 .. method:: Popen.poll()
 
    Check if child process has terminated.  Set and return
-   :attr:`~Popen.returncode` attribute.
+   :attr:`~Popen.returncode` attribute. Otherwise, returns ``None``.
 
 
 .. method:: Popen.wait(timeout=None)