fix: default input to native currency (#3456)

* fix: default to native

* chore: fix import

src/lib/hooks/swap/useSyncTokenDefaults.ts

@@ -3,6 +3,7 @@ import { nativeOnChain } from 'constants/tokens'
 import { useUpdateAtom } from 'jotai/utils'
 import useActiveWeb3React from 'lib/hooks/useActiveWeb3React'
 import { useToken } from 'lib/hooks/useCurrency'
+import useNativeCurrency from 'lib/hooks/useNativeCurrency'
 import { Field, Swap, swapAtom } from 'lib/state/swap'
 import { useCallback, useLayoutEffect, useState } from 'react'
 
@@ -18,7 +19,7 @@ export interface TokenDefaults {
 function useDefaultToken(
   defaultAddress: DefaultAddress | undefined,
   chainId: number | undefined
-): Currency | null | undefined {
+): Currency | undefined {
   let address = undefined
   if (typeof defaultAddress === 'string') {
     address = defaultAddress
@@ -29,7 +30,7 @@ function useDefaultToken(
   if (chainId && address === 'NATIVE') {
     return nativeOnChain(chainId)
   }
-  return token
+  return token ?? undefined
 }
 
 export default function useSyncTokenDefaults({
@@ -40,14 +41,18 @@ export default function useSyncTokenDefaults({
 }: TokenDefaults) {
   const updateSwap = useUpdateAtom(swapAtom)
   const { chainId } = useActiveWeb3React()
-  const defaultInputToken = useDefaultToken(defaultInputTokenAddress, chainId)
+  const nativeCurrency = useNativeCurrency()
   const defaultOutputToken = useDefaultToken(defaultOutputTokenAddress, chainId)
+  const defaultInputToken =
+    useDefaultToken(defaultInputTokenAddress, chainId) ??
+    // Default the input token to the native currency if it is not the output token.
+    (defaultOutputToken === nativeCurrency ? nativeCurrency : undefined)
 
   const setToDefaults = useCallback(() => {
     const defaultSwapState: Swap = {
       amount: '',
-      [Field.INPUT]: defaultInputToken || undefined,
-      [Field.OUTPUT]: defaultOutputToken || undefined,
+      [Field.INPUT]: defaultInputToken,
+      [Field.OUTPUT]: defaultOutputToken,
       independentField: Field.INPUT,
     }
     if (defaultInputToken && defaultInputAmount) {