fix: get-session response null error

apps/mobile/src/store/user/store.ts

@@ -25,11 +25,15 @@ class UserSyncService {
     }>("/better-auth/get-session", {
       method: "GET",
     })
-    immerSet((state) => {
-      state.whoami = res.user
-    })
-    userActions.upsertMany([res.user])
-    return res.user
+    if (res) {
+      immerSet((state) => {
+        state.whoami = res.user
+      })
+      userActions.upsertMany([res.user])
+      return res.user
+    } else {
+      return null
+    }
   }
 }