Crash report: `Error: invalid BigNumber string (argument="value", value="erc721", code=INVALID_ARGUMENT, version=bignumber/5.6.0)`

URL

https://app.uniswap.org/#/swap?outputCurrency=&chain=mainnet

swap state

{
  "INPUT": {
    "currencyId": "ETH"
  },
  "OUTPUT": {
    "currencyId": null
  },
  "independentField": "INPUT",
  "typedValue": "",
  "recipient": null
}

Error

Error: invalid BigNumber string (argument="value", value="erc721", code=INVALID_ARGUMENT, version=bignumber/5.6.0)

Stacktrace

Error: invalid BigNumber string (argument="value", value="erc721", code=INVALID_ARGUMENT, version=bignumber/5.6.0)
    at e.value (https://app.uniswap.org/static/js/3.41edfc8a.chunk.js:2:83145)
    at e.value (https://app.uniswap.org/static/js/3.41edfc8a.chunk.js:2:83289)
    at e.value (https://app.uniswap.org/static/js/3.41edfc8a.chunk.js:2:83368)
    at Function.value (https://app.uniswap.org/static/js/3.41edfc8a.chunk.js:2:173013)
    at Qn (https://app.uniswap.org/static/js/main.19d4c78b.chunk.js:1:365204)
    at Hn (https://app.uniswap.org/static/js/main.19d4c78b.chunk.js:1:364034)
    at https://app.uniswap.org/static/js/main.19d4c78b.chunk.js:1:366279
    at Zn (https://app.uniswap.org/static/js/main.19d4c78b.chunk.js:1:366502)
    at oa (https://app.uniswap.org/static/js/3.41edfc8a.chunk.js:2:1938523)
    at za (https://app.uniswap.org/static/js/3.41edfc8a.chunk.js:2:1948090)

Device data

{
  "ua": "Mozilla/5.0 (Linux; Android 11; moto g pure Build/RRHS31.Q3-46-110-2; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/98.0.4758.101 Mobile Safari/537.36 MdsApp/5.0.3 MathWallet/5.0.3",
  "browser": {
    "name": "Chrome WebView",
    "version": "98.0.4758.101",
    "major": "98"
  },
  "engine": {
    "name": "Blink",
    "version": "98.0.4758.101"
  },
  "os": {
    "name": "Android",
    "version": "11"
  },
  "device": {
    "vendor": "Motorola",
    "model": "moto g pure",
    "type": "mobile"
  },
  "cpu": {}
}

Start by reproducing the crash at the reported swap URL with the supplied swap state, then use the JavaScript stack trace to locate the failing path. Investigate why the value "erc721" reaches BigNumber parsing; done means the swap page no longer crashes for this input and the behavior is covered by an appropriate regression check.