packages/config: flip around must* and get* to get* and getOptional*

packages/cli/src/lib/bundler/config.ts

@@ -33,9 +33,6 @@ import { BundlingOptions, BackendBundlingOptions } from './types';
 
 export function resolveBaseUrl(config: Config): URL {
   const baseUrl = config.getString('app.baseUrl');
-  if (!baseUrl) {
-    throw new Error('app.baseUrl must be set in config');
-  }
   try {
     return new URL(baseUrl, 'http://localhost:3000');
   } catch (error) {
@@ -52,9 +49,6 @@ export function createConfig(
   const { plugins, loaders } = transforms(options);
 
   const baseUrl = options.config.getString('app.baseUrl');
-  if (!baseUrl) {
-    throw new Error('app.baseUrl must be set in config');
-  }
   const validBaseUrl = new URL(baseUrl, 'https://backstage-app.dev');
 
   if (checksEnabled) {