metamask-extension/app/scripts/migrations/030.js

// next version number
const version = 30

/*

removes invalid chaids from preferences and networkController for custom rpcs

*/

const clone = require('clone')

module.exports = {
  version,

  migrate: async function (originalVersionedData) {
    const versionedData = clone(originalVersionedData)
    versionedData.meta.version = version
    const state = versionedData.data
    const newState = transformState(state)
    versionedData.data = newState
    return versionedData
  },
}

function transformState (state) {
  const newState = state

  const frequentRpcListDetail = newState.PreferencesController.frequentRpcListDetail
  if (frequentRpcListDetail) {
    frequentRpcListDetail.forEach((rpc, index) => {
      if (!!rpc.chainId && Number.isNaN(parseInt(rpc.chainId))) {
        delete frequentRpcListDetail[index].chainId
      }
    })
    newState.PreferencesController.frequentRpcListDetail = frequentRpcListDetail
  }

  if (newState.NetworkController.network && Number.isNaN(parseInt(newState.NetworkController.network))) {
    delete newState.NetworkController.network
  }

  if (newState.NetworkController.provider && newState.NetworkController.provider.chainId && Number.isNaN(parseInt(newState.NetworkController.provider.chainId))) {
    delete newState.NetworkController.provider.chainId
  }

  return newState
}