From f41381a5fb85bd061897408ad4bc133e928f8850 Mon Sep 17 00:00:00 2001
From: Patrick Cloke <clokep@users.noreply.github.com>
Date: Wed, 12 Jul 2023 08:39:25 -0400
Subject: [PATCH] Fix running with an empty experimental features section.
 (#15925)

---
 changelog.d/15925.bugfix | 1 +
 synapse/config/auth.py   | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)
 create mode 100644 changelog.d/15925.bugfix

diff --git a/changelog.d/15925.bugfix b/changelog.d/15925.bugfix
new file mode 100644
index 000000000000..e3ef783576fd
--- /dev/null
+++ b/changelog.d/15925.bugfix
@@ -0,0 +1 @@
+Fix a bug introduced in 1.86.0 where Synapse starting with an empty `experimental_features` configuration setting.
diff --git a/synapse/config/auth.py b/synapse/config/auth.py
index c7ab428f28af..3b4c77f5727a 100644
--- a/synapse/config/auth.py
+++ b/synapse/config/auth.py
@@ -31,7 +31,7 @@ def read_config(self, config: JsonDict, **kwargs: Any) -> None:
 
         # The default value of password_config.enabled is True, unless msc3861 is enabled.
         msc3861_enabled = (
-            config.get("experimental_features", {})
+            (config.get("experimental_features") or {})
             .get("msc3861", {})
             .get("enabled", False)
         )