bpo-37206: Unrepresentable default values no longer represented as None. (GH-13933)

In ArgumentClinic, value "NULL" should now be used only for unrepresentable default values
(like in the optional third parameter of getattr). "None" should be used if None is accepted
as argument and passing None has the same effect as not passing the argument at all.
diff --git a/Objects/clinic/bytearrayobject.c.h b/Objects/clinic/bytearrayobject.c.h
index ad8ed7e..0557707 100644
--- a/Objects/clinic/bytearrayobject.c.h
+++ b/Objects/clinic/bytearrayobject.c.h
@@ -868,7 +868,7 @@
 }
 
 PyDoc_STRVAR(bytearray_hex__doc__,
-"hex($self, /, sep=None, bytes_per_sep=1)\n"
+"hex($self, /, sep=<unrepresentable>, bytes_per_sep=1)\n"
 "--\n"
 "\n"
 "Create a str of hexadecimal numbers from a bytearray object.\n"
@@ -1011,4 +1011,4 @@
 {
     return bytearray_sizeof_impl(self);
 }
-/*[clinic end generated code: output=09df354d3374dfb2 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=508dce79cf2dffcc input=a9049054013a1b77]*/
diff --git a/Objects/clinic/bytesobject.c.h b/Objects/clinic/bytesobject.c.h
index 7e2ce1a..22024ab 100644
--- a/Objects/clinic/bytesobject.c.h
+++ b/Objects/clinic/bytesobject.c.h
@@ -688,7 +688,7 @@
 }
 
 PyDoc_STRVAR(bytes_hex__doc__,
-"hex($self, /, sep=None, bytes_per_sep=1)\n"
+"hex($self, /, sep=<unrepresentable>, bytes_per_sep=1)\n"
 "--\n"
 "\n"
 "Create a str of hexadecimal numbers from a bytes object.\n"
@@ -755,4 +755,4 @@
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=dbed3c3ff6faa382 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=ca60dfccf8d51e88 input=a9049054013a1b77]*/
diff --git a/Objects/clinic/dictobject.c.h b/Objects/clinic/dictobject.c.h
index b87244d..7395e3b 100644
--- a/Objects/clinic/dictobject.c.h
+++ b/Objects/clinic/dictobject.c.h
@@ -117,10 +117,10 @@
 }
 
 PyDoc_STRVAR(dict_pop__doc__,
-"pop($self, key, default=None, /)\n"
+"pop($self, key, default=<unrepresentable>, /)\n"
 "--\n"
 "\n"
-"Remove specified key and return the corresponding value.\n"
+"D.pop(k[,d]) -> v, remove specified key and return the corresponding value.\n"
 "\n"
 "If key is not found, default is returned if given, otherwise KeyError is raised");
 
@@ -190,4 +190,4 @@
 {
     return dict___reversed___impl(self);
 }
-/*[clinic end generated code: output=0fd5cafc61a51d3c input=a9049054013a1b77]*/
+/*[clinic end generated code: output=4d98145508da8fa3 input=a9049054013a1b77]*/
diff --git a/Objects/clinic/floatobject.c.h b/Objects/clinic/floatobject.c.h
index 6515d11..b684ba0 100644
--- a/Objects/clinic/floatobject.c.h
+++ b/Objects/clinic/floatobject.c.h
@@ -56,7 +56,7 @@
 float___round__(PyObject *self, PyObject *const *args, Py_ssize_t nargs)
 {
     PyObject *return_value = NULL;
-    PyObject *o_ndigits = NULL;
+    PyObject *o_ndigits = Py_None;
 
     if (!_PyArg_CheckPositional("__round__", nargs, 0, 1)) {
         goto exit;
@@ -351,4 +351,4 @@
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=cc8098eb73f1a64c input=a9049054013a1b77]*/
+/*[clinic end generated code: output=1676433b9f04fbc9 input=a9049054013a1b77]*/
diff --git a/Objects/clinic/memoryobject.c.h b/Objects/clinic/memoryobject.c.h
index 64fce10..75ac201 100644
--- a/Objects/clinic/memoryobject.c.h
+++ b/Objects/clinic/memoryobject.c.h
@@ -3,7 +3,7 @@
 [clinic start generated code]*/
 
 PyDoc_STRVAR(memoryview_hex__doc__,
-"hex($self, /, sep=None, bytes_per_sep=1)\n"
+"hex($self, /, sep=<unrepresentable>, bytes_per_sep=1)\n"
 "--\n"
 "\n"
 "Return the data in the buffer as a str of hexadecimal numbers.\n"
@@ -71,4 +71,4 @@
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=5e44e2bcf01057b5 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=ee265a73f68b0077 input=a9049054013a1b77]*/
diff --git a/Objects/clinic/unicodeobject.c.h b/Objects/clinic/unicodeobject.c.h
index cb35087..c7d6edb 100644
--- a/Objects/clinic/unicodeobject.c.h
+++ b/Objects/clinic/unicodeobject.c.h
@@ -630,7 +630,7 @@
 unicode_lstrip(PyObject *self, PyObject *const *args, Py_ssize_t nargs)
 {
     PyObject *return_value = NULL;
-    PyObject *chars = NULL;
+    PyObject *chars = Py_None;
 
     if (!_PyArg_CheckPositional("lstrip", nargs, 0, 1)) {
         goto exit;
@@ -664,7 +664,7 @@
 unicode_rstrip(PyObject *self, PyObject *const *args, Py_ssize_t nargs)
 {
     PyObject *return_value = NULL;
-    PyObject *chars = NULL;
+    PyObject *chars = Py_None;
 
     if (!_PyArg_CheckPositional("rstrip", nargs, 0, 1)) {
         goto exit;
@@ -1045,7 +1045,7 @@
 }
 
 PyDoc_STRVAR(unicode_maketrans__doc__,
-"maketrans(x, y=None, z=None, /)\n"
+"maketrans(x, y=<unrepresentable>, z=<unrepresentable>, /)\n"
 "--\n"
 "\n"
 "Return a translation table usable for str.translate().\n"
@@ -1232,4 +1232,4 @@
 {
     return unicode_sizeof_impl(self);
 }
-/*[clinic end generated code: output=d9a6ee45ddd0ccfd input=a9049054013a1b77]*/
+/*[clinic end generated code: output=5e15747f78f18329 input=a9049054013a1b77]*/