Expected Behavior:
Measurement with provided string is correctly escaped and written to the DB

Current Behavior:
Operation results in Cannot read property 'escapeChar' of undefined error.

Steps/Code to Reproduce the Problem:

1. The "minimal" string i was able to reproduce the issue with {"prop":"{\"str\":\"test\"}"}
2. This type of string escaping is the result of double stringification via JSON.stringify() (object containing a valid JSON string is stringified again)
3. Partially-pseudo code to reproduce the issue (i don't really have any TS experience, i have adopted the 1.8 TS example for this, apologies/did what i could here)

import {ClientOptions, InfluxDB, Point} from '@influxdata/influxdb-client'

const username = 'username'
const password = 'password'

const database = 'telegraf'
const retentionPolicy = 'autogen'

const bucket = `${database}/${retentionPolicy}`

const clientOptions: ClientOptions = {
  url: 'http://localhost:8086',
  token: `${username}:${password}`,
}

const influxDB = new InfluxDB(clientOptions)
const writeAPI = influxDB.getWriteApi('', bucket)

const point = new Point('testMeasurement');

// THE IMPORTANT PART
point.stringField('testField', '{"prop":"{\"str\":\"test\"}"}');

writeAPI.writePoint(point)
writeAPI
  .close()
  .then(() => console.log('FINISHED'))
  .catch(error => {
    console.error(error)
  })

The very likely cause is an edge case related to #205 on https://github.com/influxdata/influxdb-client-js/blob/master/packages/core/src/util/escape.ts#L60

Specifications:

• Version: InfluxDB 1.8.1 & influxdb-client-js 1.6.0
• Platform: Linux & node.js 12.18.3