Cannot Read for Each property of null while displaying Gallery Images - node.js

Question

This is my Product method for displaying all the PRODUCTS at the Home PAGE WITH respect to its Categories
//GET Products DEtails
router.get('/:category/:product',function(req,res){
var galleryImages=null;
models.Product.findOne({
where:{slug:req.params.product}
})
.then(function(product){
var galleryDir='public/product_images/' + product.id + '/gallery';
fs.readdir(galleryDir,function(files){
galleryImages=files;
res.render('product',{
title:product.title,
p:product,
galleryImages:galleryImages,
})
})
})
});
This is mine Product.ejs file for displaying it the P.Images is working above but the forEach loop is not working Cannot read property forEach of Null the Path for mine Gallery images is Correct
<% include layouts/header %>
<div class="row">
<h1 class="page-header"><%= p.title %></h1>
<div class="col-xs-12 col-md-5">
<img class="spi" src="/product_images/<%= p.id %>/<%= p.images %>" alt="">
<br>
</div>
<div class="col-xs-12 col-md-7">
<p><%= p.desc %></p>
<p>$<%= parseFloat(p.price).toFixed(2) %></p>
<p>Add To Cart</p>
</div>
<div class="col-xs-12">
<ul class="gallery">
<% galleryImages.forEach(function(images){ %>
<% if (images != "thumbs") { %>
<li>
<!--<a data-fancybox="gallery" href="/product_images/<%= p.id %>/gallery/<%= images %>"> -->
<img src="/product_images/<%= p.id %>/gallery/thumbs/<%= images %>" alt="">
</a>
</li>
<% } %>
<% }); %>
</ul>
</div>
</div>
<!--
- will gave Content Where as = will gave Html <P>tag in the Browser</P> -->
<% include layouts/footer %>

Answer 1

This is my products.js after try. It worked
/*
* GET product details by category
*/
router.get('/:category/:product', function (req,res){
Product.findOne({slug: req.params.product}, function (err, product) {
if(!product) { //if product not exist in db
return res.status(404).send('Product not found');
}else{
var galleryDir = 'public/product_images/' + product._id + '/gallery';
fs.readdir(galleryDir, function (err, files) {
if (err) {
console.log(err);
} else {
galleryImages = files;
res.render('product', {
title: product.title,
p: product,
galleryImages: galleryImages
});
}
});
}
});
});