Can not import / null

'react-native': '0.59.8',
npm: '6.9.0',
react-native-fs: 2.16.1

When trying to import as per doc:
import * as RNFS from 'react-native-fs';
just this import is causing error can not import null

When trying to use this in my code:
var RNFS = require('react-native-fs');
RNFS.readFile(selectedImage.uri, 'base64').then(res => {
console.log("File read");
})
RNFS.readFile is also a null/undefined:
[TypeError: undefined is not an object (evaluating 'RNFS.readFile')]

I have installed for my project:
npm install --save react-native-fs
react-native link react-native-fs

How to import RNFS and get it working ?

Thanks