merge multiple videos to a single .mp4 files using fluent-ffmpeg

Question

Version information

fluent-ffmpeg version: 2.1.2
ffmpeg version:4
OS:linux mint

Code to reproduce

var fluent_ffmpeg = require("fluent-ffmpeg");

var mergedVideo = fluent_ffmpeg();

mergedVideo
  .mergeAdd('./Video1.mp4')
  .mergeAdd('./Video2.mp4')
  // .inputOptions(['-loglevel error','-hwaccel vdpau'])
  // .outputOptions('-c:v h264_nvenc')
  .on('error', function(err) {
      console.log('Error ' + err.message);
  })
  .on('end', function() {
      console.log('Finished!');
  })
  .mergeToFile('./mergedVideo8.mp4', '/tmp');

When I run this code, then I get conversion failed error.

Observed results

Error ffmpeg exited with code 1: Error reinitializing filters!
Failed to inject frame into filter network: Invalid argument
Error while processing the decoded data for stream #3:0
Conversion failed!

I have tried the same conversion using the command line:

ffmpeg -f concat -i textfile -c copy -fflags +genpts merged8.mp4

Where textfile has the following content-

file 'Video1.mp4'
file 'Video2.mp4'

And I was able to concatenate the video file. But I want to get the same result using fluent-ffmpeg.