Getting goole-charts to work in a custom card

Ehlo,

I am trying to make a custom card with a pie chart in it. I will eventually also need line charts like in the sensor or history-graph card.

I tried the following import:

import 'https://unpkg.com/@google-web-components/google-chart/google-chart.js?module'; 

It seems like it isn’t working with the error:

Uncaught DOMException: Failed to execute 'define' on 'CustomElementRegistry': this name has already been used with this registry
at https://unpkg.com/@polymer/[email protected]/lib/elements/dom-module.js?module:175:16

I am new to Polymer so I have no idea of how to get this working.
Can anybody help me on this ? Thanks in advance !