Update types to match reality (#3271)

src/client.ts

@@ -7471,7 +7471,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      * Set the identity server URL of this client
      * @param url - New identity server URL
      */
-    public setIdentityServerUrl(url: string): void {
+    public setIdentityServerUrl(url?: string): void {
         this.idBaseUrl = utils.ensureNoTrailingSlash(url);
         this.http.setIdBaseUrl(this.idBaseUrl);
     }

src/http-api/fetch.ts

@@ -66,7 +66,7 @@ export class FetchHttpApi<O extends IHttpOpts> {
      * Sets the base URL for the identity server
      * @param url - The new base url
      */
-    public setIdBaseUrl(url: string): void {
+    public setIdBaseUrl(url?: string): void {
         this.opts.idBaseUrl = url;
     }
 

src/pushprocessor.ts

@@ -589,7 +589,7 @@ export class PushProcessor {
      * @internal
      */
     public static partsForDottedKey(str: string): string[] {
-        const result = [];
+        const result: string[] = [];
 
         // The current field and whether the previous character was the escape
         // character (a backslash).