Unable to build this web component

[Piiit]

Hi,
I try to build this web component, but get the following error:

[!] (plugin commonjs) TypeError: The "path" argument must be of type string. Received type undefined
 TypeError [ERR_INVALID_ARG_TYPE] [ERR_INVALID_ARG_TYPE]: The "path" argument must be of type string. Received type undefined
     at validateString (internal/validators.js:112:11)
     at Object.resolve (path.js:981:7)
     at normalizeRelativeExternalId (/code/node_modules/rollup/dist/shared/node-entry.js:12143:38)
     at ModuleLoader.normalizeResolveIdResult (/code/node_modules/rollup/dist/shared/node-entry.js:12449:18)
     at ModuleLoader.<anonymous> (/code/node_modules/rollup/dist/shared/node-entry.js:12259:25)
     at Generator.next (<anonymous>)
     at fulfilled (/code/node_modules/rollup/dist/shared/node-entry.js:38:28)

Any idea why this is happening?

Note: I use node:12 in a Docker environment to build it.

ps. The other 3 weather web components built fine. See https://webcomponents.opendatahub.testingmachine.eu/ for details.

Cheers and happy hacking :-)
Peter