Do not fail when returning null or undefined from an async options hook

src/rollup/rollup.ts

@@ -122,13 +122,14 @@ function applyOptionHook(watchMode: boolean) {
 		inputOptions: Promise<GenericConfigObject>,
 		plugin: Plugin
 	): Promise<GenericConfigObject> => {
-		if (plugin.options)
+		if (plugin.options) {
 			return (
-				(plugin.options.call(
+				((await plugin.options.call(
 					{ meta: { rollupVersion, watchMode } },
 					await inputOptions
-				) as GenericConfigObject) || inputOptions
+				)) as GenericConfigObject) || inputOptions
 			);
+		}
 
 		return inputOptions;
 	};

test/function/samples/aync-options/_config.js

@@ -0,0 +1,25 @@
+const assert = require('assert');
+
+module.exports = {
+	description: 'handles async plugin options',
+	options: {
+		preserveEntrySignatures: false,
+		plugins: [
+			{
+				options(options) {
+					assert.strictEqual(options.preserveEntrySignatures, false);
+					return Promise.resolve({ ...options, preserveEntrySignatures: 'strict' });
+				}
+			},
+			{
+				options(options) {
+					assert.strictEqual(options.preserveEntrySignatures, 'strict');
+					return Promise.resolve(null);
+				}
+			}
+		]
+	},
+	exports(exports) {
+		assert.strictEqual(exports.foo, 1);
+	}
+};

test/function/samples/aync-options/main.js

@@ -0,0 +1 @@
+export const foo = 1;