src/vs/workbench/api/browser/mainThreadDocuments.ts/MainThreadDocuments/_handleUntitledScheme
class MainThreadDocuments:	private async _handleUntitledScheme(uri: URI): Promise<URI> {
		const asLocalUri = toLocalResource(uri, this._environmentService.remoteAuthority, this._pathService.defaultUriScheme);
		const exists = await this._fileService.exists(asLocalUri);
		if (exists) {
			// don't create a new file ontop of an existing file
			return Promise.reject(new Error('file already exists'));
		}
		return await this._doCreateUntitled(Boolean(uri.path) ? uri : undefined);
	}