interface: check accessKey !== undefined

Also make it type-level optional rather than using explicit null.

Perhaps one day we will want to use undefined to denote "the thread
hasn't returned yet" and null for "GCP Storage is not configured."
Perhaps.

pkg/interface/src/logic/lib/useStorage.ts

@@ -23,7 +23,7 @@ const useStorage = (s3: S3State, gcp: GcpState,
 
   useEffect(() => {
     // prefer GCP if available, else use S3.
-    if (gcp.accessKey) {
+    if (gcp.accessKey !== undefined) {
       client.current = new GcpClient(gcp.accessKey);
     } else {
       if (!s3.credentials) {

pkg/interface/src/logic/store/store.ts

@@ -73,9 +73,7 @@ export default class GlobalStore extends BaseStore<StoreState> {
       },
       weather: {},
       userLocation: null,
-      gcp: {
-        accessKey: null
-      },
+      gcp: {},
       s3: {
         configuration: {
           buckets: new Set(),

pkg/interface/src/types/gcp-state.ts

@@ -4,5 +4,5 @@ export interface GcpToken {
 };
 
 export interface GcpState {
-  accessKey: string;
+  accessKey?: string;
 };