fix(node-resolve): error thrown with empty entry (#1893)

* Fix error thrown with empty entry while using node-resolve plugin

* Clean up test syntax

* Formatting

Author: jolyndenning

packages/node-resolve/src/index.js

@@ -152,7 +152,7 @@ export function nodeResolve(opts = {}) {
 
     const importSpecifierList = [importee];
 
-    if (importer === undefined && !importee[0].match(/^\.?\.?\//)) {
+    if (importer === undefined && importee[0] && !importee[0].match(/^\.?\.?\//)) {
       // For module graph roots (i.e. when importer is undefined), we
       // need to handle 'path fragments` like `foo/bar` that are commonly
       // found in rollup config files. If importee doesn't look like a

packages/node-resolve/test/test.mjs

@@ -743,3 +743,15 @@ test('allow other plugins to take over resolution', async (t) => {
     ]
   });
 });
+
+test('error message for invalid entry', async (t) => {
+  const error = await t.throwsAsync(() =>
+    rollup({
+      input: '',
+      onwarn: failOnWarn(t),
+      plugins: [nodeResolve()]
+    })
+  );
+
+  t.is(error.message, `Could not resolve entry module "".`);
+});