Fixed #25784 -- Prevented an exception on collectstatic help

Made the `manage.py help collectstatic` don't fail if the `STATIC_ROOT`
setting is empty.

django/contrib/staticfiles/management/commands/collectstatic.py

@@ -9,6 +9,7 @@
 from django.core.management.base import BaseCommand, CommandError
 from django.core.management.color import no_style
 from django.utils.encoding import smart_text
+from django.utils.functional import cached_property
 from django.utils.six.moves import input
 
 
@@ -28,12 +29,14 @@ def __init__(self, *args, **kwargs):
         self.post_processed_files = []
         self.storage = staticfiles_storage
         self.style = no_style()
+
+    @cached_property
+    def local(self):
         try:
             self.storage.path('')
         except NotImplementedError:
-            self.local = False
-        else:
-            self.local = True
+            return False
+        return True
 
     def add_arguments(self, parser):
         parser.add_argument('--noinput', '--no-input',

tests/staticfiles_tests/test_management.py

@@ -6,6 +6,8 @@
 import tempfile
 import unittest
 
+from admin_scripts.tests import AdminScriptTestCase
+
 from django.conf import settings
 from django.contrib.staticfiles import storage
 from django.contrib.staticfiles.management.commands import collectstatic
@@ -130,6 +132,18 @@ def test_local_storage_detection_helper(self):
             storage.staticfiles_storage = staticfiles_storage
 
 
+class TestCollectionHelpSubcommand(AdminScriptTestCase):
+    @override_settings(STATIC_ROOT=None)
+    def test_missing_settings_dont_prevent_help(self):
+        """
+        Even if the STATIC_ROOT setting is not set, one can still call the
+        `manage.py help collectstatic` command.
+        """
+        self.write_settings('settings.py', apps=['django.contrib.staticfiles'])
+        out, err = self.run_manage(['help', 'collectstatic'])
+        self.assertNoOutput(err)
+
+
 class TestCollection(CollectionTestCase, TestDefaults):
     """
     Test ``collectstatic`` management command.