failing.js

// put this in the ethers-airdrop root dir and run with `node failing.js`
// 3rd account has a proof with an `undefined`

var AirDrop = require('./index.js')

let a = new AirDrop({
  "0x7b14ff3a4b7f1585860d8e7b5935697ae2a1fb2a": "0x392d2e2bda9c0000",
  "0xe5c646116d310bac2b21c8cf989b0f955606d011": "0x58d15e17628000",
  "0xf430775da1df51693ecc1fe6c4934d9339613b4d": "0x00",
})

Object.keys(a.balances).forEach((account, index) => {
  console.log(`${index} - ${account}`)
  console.log(a.getMerkleProof(index))
})

/*
Output
0 - 0x7b14ff3a4b7f1585860d8e7b5935697ae2a1fb2a
[
  '0xfc5d524ac19366b4597a17b90be6bdbf01349b4e6d1b2bb7f2ee77516ebba0ff',
  '0x23a091012b37d625af4ac04fa31cae8e40c833e219b23e1d1df23475b9d09873'
]
1 - 0xe5c646116d310bac2b21c8cf989b0f955606d011
[
  '0xd4744dc1f9d42039ff90cdbc7a65f104e33c08795d753d35fe66c4473bdfd322',
  '0x23a091012b37d625af4ac04fa31cae8e40c833e219b23e1d1df23475b9d09873'
]
2 - 0xf430775da1df51693ecc1fe6c4934d9339613b4d
[
  undefined,
  '0xa74e9fe2d08028c4afbf84b54a053dc3ec891e2872657ff8bfb67cff7f1925ba'
]
*/