org settings: Handle NEW_USER_BOT not being set.

If NEW_USER_BOT is not configured in organization, then disable setting
for selecting stream for new user notification.

zerver/tests/test_home.py

@@ -93,6 +93,7 @@ class HomeTest(ZulipTestCase):
             "narrow_stream",
             "needs_tutorial",
             "never_subscribed",
+            "new_user_bot_configured",
             "night_mode",
             "password_min_guesses",
             "password_min_length",

zerver/tests/test_realm.py

@@ -216,6 +216,10 @@ class RealmTest(ZulipTestCase):
 
         new_signup_notifications_stream_id = 4
         req = dict(signup_notifications_stream_id = ujson.dumps(new_signup_notifications_stream_id))
+        with self.settings(NEW_USER_BOT=None):
+            result = self.client_patch("/json/realm", req)
+            self.assert_json_error(result, 'NEW_USER_BOT must configured first.')
+
         result = self.client_patch('/json/realm', req)
         self.assert_json_success(result)
         realm = get_realm('zulip')

zerver/views/home.py

@@ -173,6 +173,7 @@ def home_real(request: HttpRequest) -> HttpResponse:
     # These end up in a global JavaScript Object named 'page_params'.
     page_params = dict(
         # Server settings.
+        new_user_bot_configured = settings.NEW_USER_BOT is not None,
         development_environment = settings.DEVELOPMENT,
         debug_mode            = settings.DEBUG,
         test_suite            = settings.TEST_SUITE,

zerver/views/realm.py

@@ -2,7 +2,7 @@
 from typing import Any, Dict, Optional, List, Text
 from django.http import HttpRequest, HttpResponse
 from django.utils.translation import ugettext as _
-
+from django.conf import settings
 from zerver.decorator import require_realm_admin, to_non_negative_int, to_not_negative_int_or_none
 from zerver.lib.actions import (
     do_set_realm_message_editing,
@@ -59,6 +59,8 @@ def update_realm(
         return json_error(_("Realm name is too long."))
     if authentication_methods is not None and True not in list(authentication_methods.values()):
         return json_error(_("At least one authentication method must be enabled."))
+    if signup_notifications_stream_id is not None and settings.NEW_USER_BOT is None:
+        return json_error(_("NEW_USER_BOT must configured first."))
 
     # The user of `locals()` here is a bit of a code smell, but it's
     # restricted to the elements present in realm.property_types.