fix gulp package #3693

gulpfile.js

@@ -1,3 +1,4 @@
+const fs = require('fs');
 const pkg = require('./package.json')
 const glob = require('glob')
 const yargs = require('yargs')
@@ -274,22 +275,23 @@ gulp.task('default', gulp.series(gulp.parallel('js', 'css', 'plugins'), 'test'))
 
 gulp.task('build', gulp.parallel('js', 'css', 'plugins'))
 
-gulp.task('package', gulp.series(() =>
+gulp.task('package', gulp.series(async () => {
 
-    gulp.src(
-        [
+    let dirs = [
         './index.html',
         './dist/**',
-            './lib/**',
-            './images/**',
         './plugin/**',
-            './**/*.md'
-        ],
-        { base: './' }
-    )
+        './*/*.md'
+    ];
+
+    if (fs.existsSync('./lib')) dirs.push('./lib/**');
+    if (fs.existsSync('./images')) dirs.push('./images/**');
+    if (fs.existsSync('./slides')) dirs.push('./slides/**');
+
+    return gulp.src( dirs, { base: './' } )
     .pipe(zip('reveal-js-presentation.zip')).pipe(gulp.dest('./'))
 
-))
+}))
 
 gulp.task('reload', () => gulp.src(['index.html'])
     .pipe(connect.reload()));