'npm' TypeError: Cannot read property 'toString' of undefined

NPM script view is not loaded on theia v1.5.0 master build locally.
$ node --version
v12.18.3

commit d7605539b35a4bc0a905234572dd78ff88904378 (HEAD -> master, origin/master, origin/HEAD)
Author: vince-fugnitto <vincent.fugnitto@ericsson.com>
Date:   Tue Sep 1 12:20:47 2020 -0400
root INFO [2e1c7d9f-2a20-4021-b921-8d255bbf2543] Start of 71 plugins took: 605.9 ms
bundle.js:139956 root ERROR Failed to fetch children for 'npm' TypeError: Cannot read property 'toString' of undefined
    at ProvidedTaskConfigurations.push.../../packages/task/lib/browser/provided-task-configurations.js.ProvidedTaskConfigurations.cacheTasks (http://localhost:3000/27.bundle.js:413:49)
    at ProvidedTaskConfigurations.<anonymous> (http://localhost:3000/27.bundle.js:296:30)
    at step (http://localhost:3000/27.bundle.js:188:23)
    at Object.next (http://localhost:3000/27.bundle.js:169:53)
    at fulfilled (http://localhost:3000/27.bundle.js:160:58)
log @ bundle.js:139956

@chakraborty-slx this is the master build, the vscode-npm (scripts) extension is working correctly:

Are you using a different version than that of the main repository?

I am using the master branch too.

I am using node v12 ,
chakraborty@precision7530:~/web/theia/theia$ node --version
v12.18.3
chakraborty@precision7530:~/web/theia/theia$ yarn version
yarn version v1.22.4

instructions from https://github.com/eclipse-theia/theia/blob/master/doc/Developing.md#run-the-browser-based-example-application

yarn 

yarn rebuild:browser

cd examples/broswer

yarn run start

I have put an vscode vsix file which contributes tasks using

vscode.tasks.registerTaskProvider

maybe the reason for this issue. I am able to see the NPM script view if i remove the plugin.