fix: errors in profileStorageUsed function (#2494)

## Why is this change needed?

Describe why this issue should be fixed and link to any relevant design
docs, issues or other relevant items.

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<!-- start pr-codex -->

---

## PR-Codex overview
This PR focuses on enhancing the handling of potentially `undefined`
values in the `KeysProfile` constructor by providing a default empty
string when the value is `undefined`.

### Detailed summary
- Updated the `prefixKeys` array mapping to use `|| ""` for
`RootPrefix[i]?.toString()`.
- Updated the `userPostfixKeys` array mapping to use `|| ""` for
`UserPostfix[i]?.toString()`.

> ✨ Ask PR-Codex anything about this PR by commenting with `/codex {your
question}`

<!-- end pr-codex -->

apps/hubble/src/profile/profile.ts

@@ -280,12 +280,12 @@ export async function profileStorageUsed(rocksDB: RocksDB, fidProfileFileName?:
   const allKeys = new KeysProfile("All Keys");
   const prefixKeys = Array.from(
     { length: getMaxValue(RootPrefix) + 1 },
-    (_v, i: number) => new KeysProfile(RootPrefix[i]?.toString()),
+    (_v, i: number) => new KeysProfile(RootPrefix[i]?.toString() || ""),
   );
 
   const userPostfixKeys = Array.from(
     { length: getMaxValue(UserPostfix) + 1 },
-    (_v, i: number) => new KeysProfile(UserPostfix[i]?.toString()),
+    (_v, i: number) => new KeysProfile(UserPostfix[i]?.toString() || ""),
   );
 
   const onchainPostfixKeys = Array.from(