Fix a NULL dereference.

Author: serhiy-storchaka

Lib/test/test_cmd_line.py

@@ -198,7 +198,7 @@ def test_run_module_bug1764407(self):
         p.stdin.write(b'Timer\n')
         p.stdin.write(b'exit()\n')
         data = kill_python(p)
-        self.assertTrue(data.find(b'1 loop') != -1)
+        self.assertIn(b'1 loop', data)
         self.assertTrue(data.find(b'__main__.Timer') != -1)
 
     def test_relativedir_bug46421(self):

Python/_warnings.c

@@ -180,17 +180,17 @@ check_matched(PyInterpreterState *interp, PyObject *obj, PyObject *arg, PyObject
     if (obj == Py_None)
         return 1;
 
-    /* An internal plain text default filter must match exactly */
-    if (PyUnicode_CheckExact(obj)) {
-        int cmp_result = PyUnicode_Compare(obj, arg);
-        if (cmp_result == -1 && PyErr_Occurred()) {
-            return -1;
+    if (arg != NULL) {
+        /* An internal plain text default filter must match exactly */
+        if (PyUnicode_CheckExact(obj)) {
+            int cmp_result = PyUnicode_Compare(obj, arg);
+            if (cmp_result == -1 && PyErr_Occurred()) {
+                return -1;
+            }
+            return !cmp_result;
         }
-        return !cmp_result;
-    }
 
-    /* Otherwise assume a regex filter and call its match() method */
-    if (arg != NULL) {
+        /* Otherwise assume a regex filter and call its match() method */
         result = PyObject_CallMethodOneArg(obj, &_Py_ID(match), arg);
     }
     else {