From a64c29926efd8460dfc9561d761898197638973d Mon Sep 17 00:00:00 2001
From: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>
Date: Wed, 27 Jan 2021 11:49:31 +0000
Subject: [PATCH] Pass a dict, instead of None, to modules if a None config is
 specified in the homeserver config (#9229)

If a Synapse module's config block were empty in YAML, thus being translated to a `Nonetype` in Python, then some modules could fail as that None ends up getting passed to their `parse_config` method. Modules are expected to accept a `dict` instead.

This PR ensures that if the user does end up specifying an empty config block (such as what [the default oidc config in the sample config](https://github.com/matrix-org/synapse/blob/5310808d3bebd17275355ecd474bc013e8c7462d/docs/sample_config.yaml#L1816-L1845) states) then `None` is not passed to the module. An empty dict is passed instead.

This code assumes that no existing modules are relying on receiving a `None` config block, but I'd really hope that they aren't.
---
 changelog.d/9229.bugfix       | 1 +
 synapse/util/module_loader.py | 3 ++-
 2 files changed, 3 insertions(+), 1 deletion(-)
 create mode 100644 changelog.d/9229.bugfix

diff --git a/changelog.d/9229.bugfix b/changelog.d/9229.bugfix
new file mode 100644
index 0000000000..3ed32291de
--- /dev/null
+++ b/changelog.d/9229.bugfix
@@ -0,0 +1 @@
+Fix a bug where `None` was passed to Synapse modules instead of an empty dictionary if an empty module `config` block was provided in the homeserver config.
\ No newline at end of file
diff --git a/synapse/util/module_loader.py b/synapse/util/module_loader.py
index 1ee61851e4..09b094ded7 100644
--- a/synapse/util/module_loader.py
+++ b/synapse/util/module_loader.py
@@ -49,7 +49,8 @@ def load_module(provider: dict, config_path: Iterable[str]) -> Tuple[Type, Any]:
     module = importlib.import_module(module)
     provider_class = getattr(module, clz)
 
-    module_config = provider.get("config")
+    # Load the module config. If None, pass an empty dictionary instead
+    module_config = provider.get("config") or {}
     try:
         provider_config = provider_class.parse_config(module_config)
     except jsonschema.ValidationError as e: