HttpClient.getFeesAsync mutates params

[nightwolfz]

Example

Object.assign(feesRequest, {
  makerTokenAmount: new BigNumber(makerTokenAmount), // units offered
  takerTokenAmount: new BigNumber(takerTokenAmount), // units requested
})
console.log(typeof feesRequest.makerTokenAmount) // BigNumber

const feesResponse = await relayerClient.getFeesAsync(feesRequest)

console.log(typeof feesRequest.makerTokenAmount) // string

[fabioberger]

Yep, that's a bug, thanks for the heads up! Will fix.

[BMillman19]

Addressed in #296