From df24eec8bea1e8e62f3e56a032eaf0abd731f53a Mon Sep 17 00:00:00 2001
From: J M Rossy <jm.rossy@gmail.com>
Date: Wed, 24 Jan 2024 16:49:22 -0500
Subject: [PATCH] Fix address util nullish fallback handling (#3181)

### Description

Small fix for address utils

### Related issues

https://github.com/hyperlane-xyz/issues/issues/899

### Backward compatibility

Yes

### Testing

In warp UI
---
 .changeset/polite-lobsters-boil.md | 5 +++++
 typescript/utils/src/addresses.ts  | 3 ++-
 typescript/utils/src/typeof.ts     | 7 ++++---
 3 files changed, 11 insertions(+), 4 deletions(-)
 create mode 100644 .changeset/polite-lobsters-boil.md

diff --git a/.changeset/polite-lobsters-boil.md b/.changeset/polite-lobsters-boil.md
new file mode 100644
index 0000000000..04f60468bb
--- /dev/null
+++ b/.changeset/polite-lobsters-boil.md
@@ -0,0 +1,5 @@
+---
+'@hyperlane-xyz/utils': patch
+---
+
+Fix for address utils falsy fallbacks
diff --git a/typescript/utils/src/addresses.ts b/typescript/utils/src/addresses.ts
index 8dec0f7353..47852c4525 100644
--- a/typescript/utils/src/addresses.ts
+++ b/typescript/utils/src/addresses.ts
@@ -2,6 +2,7 @@ import { fromBech32, normalizeBech32, toBech32 } from '@cosmjs/encoding';
 import { PublicKey } from '@solana/web3.js';
 import { utils as ethersUtils } from 'ethers';
 
+import { isNullish } from './typeof';
 import { Address, HexString, ProtocolType } from './types';
 
 const EVM_ADDRESS_REGEX = /^0x[a-fA-F0-9]{40}$/;
@@ -67,7 +68,7 @@ function routeAddressUtil<T>(
 ) {
   protocol ||= getAddressProtocolType(param);
   if (protocol && fns[protocol]) return fns[protocol]!(param);
-  else if (fallback) return fallback;
+  else if (!isNullish(fallback)) return fallback;
   else throw new Error(`Unsupported protocol ${protocol}`);
 }
 
diff --git a/typescript/utils/src/typeof.ts b/typescript/utils/src/typeof.ts
index eb08c4f15a..a204981dbb 100644
--- a/typescript/utils/src/typeof.ts
+++ b/typescript/utils/src/typeof.ts
@@ -1,6 +1,7 @@
-export function isNullish<T>(val: T) {
-  if (val === null || val === undefined) return true;
-  else return false;
+export function isNullish<T>(
+  val: T,
+): val is T extends null | undefined ? T : never {
+  return val === null || val === undefined;
 }
 
 export function isNumeric(value: string | number) {