Fixed #22256 -- Replaced bad fallback for missing PATH

Thanks Baptiste Mispelon for the review.
Backport of acee46fc9 from master.

tests/user_commands/tests.py

@@ -1,8 +1,9 @@
+import os
 import sys
 
 from django.core import management
 from django.core.management import CommandError
-from django.core.management.utils import popen_wrapper
+from django.core.management.utils import find_command, popen_wrapper
 from django.test import SimpleTestCase
 from django.utils import translation
 from django.utils.six import StringIO
@@ -60,6 +61,19 @@ class CommandTests(SimpleTestCase):
             management.call_command('leave_locale_alone_true', stdout=out)
             self.assertEqual(out.getvalue(), "pl\n")
 
+    def test_find_command_without_PATH(self):
+        """
+        find_command should still work when the PATH environment variable
+        doesn't exist (#22256).
+        """
+        current_path = os.environ.pop('PATH', None)
+
+        try:
+            self.assertIsNone(find_command('_missing_'))
+        finally:
+            if current_path is not None:
+                os.environ['PATH'] = current_path
+
 
 class UtilsTests(SimpleTestCase):