gh-125196: PyUnicodeWriter_Discard(NULL) does nothing (#125222)

Author: vstinner

Doc/c-api/unicode.rst

@@ -1600,6 +1600,8 @@ object.
 
    Discard the internal Unicode buffer and destroy the writer instance.
 
+   If *writer* is ``NULL``, no operation is performed.
+
 .. c:function:: int PyUnicodeWriter_WriteChar(PyUnicodeWriter *writer, Py_UCS4 ch)
 
    Write the single Unicode character *ch* into *writer*.

Objects/listobject.c

@@ -563,9 +563,7 @@ list_repr_impl(PyListObject *v)
     return PyUnicodeWriter_Finish(writer);
 
 error:
-    if (writer != NULL) {
-        PyUnicodeWriter_Discard(writer);
-    }
+    PyUnicodeWriter_Discard(writer);
     Py_ReprLeave((PyObject *)v);
     return NULL;
 }

Objects/unicodeobject.c

@@ -13455,6 +13455,9 @@ PyUnicodeWriter_Create(Py_ssize_t length)
 
 void PyUnicodeWriter_Discard(PyUnicodeWriter *writer)
 {
+    if (writer == NULL) {
+        return;
+    }
     _PyUnicodeWriter_Dealloc((_PyUnicodeWriter*)writer);
     PyMem_Free(writer);
 }