Python 3 changed the TypeError to a ValueError

src/gevent/subprocess.py

@@ -1279,12 +1279,13 @@ def _execute_child(self, args, executable, preexec_fn, close_fds,
 
             # PyPy 2.7 7.3.6 is now producing these errors. This happens automatically
             # on Posix platforms.
-            def _check_nul(s):
+            def _check_nul(s, err_kind=(ValueError if PY3 else TypeError)):
                 if not s:
                     return
                 nul = b'\0' if isinstance(s, bytes) else '\0'
                 if nul in s:
-                    raise TypeError("argument must be a string without NUL characters")
+                    # PyPy 2 expects a TypeError; Python 3 raises ValueError always.
+                    raise err_kind("argument must be a string without NUL characters")
             def _check_env():
                 if not env:
                     return