src/vs/workbench/api/common/extHostNotebook.ts/ExtHostNotebookController/_getProviderData
class ExtHostNotebookController:	private _getProviderData(viewType: string): NotebookContentProviderData {
		const result = this._notebookContentProviders.get(viewType);
		if (!result) {
			throw new Error(`NO provider for '${viewType}'`);
		}
		return result;
	}