Improve context types (#10510)

src/contexts/SDKContext.ts

@@ -38,7 +38,10 @@ import {
     VoiceBroadcastRecordingsStore,
 } from "../voice-broadcast";
 
-export const SDKContext = createContext<SdkContextClass | undefined>(undefined);
+// This context is available to components under MatrixChat,
+// the context must not be used by components outside a SdkContextClass tree.
+// This assertion allows us to make the type not nullable.
+export const SDKContext = createContext<SdkContextClass>(null as any);
 SDKContext.displayName = "SDKContext";
 
 /**