fix: throw a proper error when no files are found

src/index.js

@@ -330,6 +330,10 @@ const restoreShebangs = (shebangs) =>
  * @throws {Error} If there's a problem while transforming a file.
  */
 const transformOutput = async (files, options) => {
+  if (!files.length) {
+    throw new Error('No files to transform were found');
+  }
+
   const transformOptions = {
     verbose: 0,
     dry: false,

tests/index.test.js

@@ -932,6 +932,20 @@ describe('index', () => {
       });
     });
 
+    it('should throw if the no files are provided', () => {
+      // Given
+      const files = [];
+      const options = {
+        input: ['src'],
+        output: 'esm',
+      };
+      expect.assertions(1);
+      // When
+      return transformOutput(files, options).catch((error) => {
+        expect(error.message).toMatch(/No files to transform were found/i);
+      });
+    });
+
     it('should remove and restore the shebang of a file', async () => {
       // Given
       const files = [