Trying to exclude Media Mail when a T-shirt is in the cart

[FaithCoder]

Looking for some direction here with scripts.  All of our products are eligible for media mail shipping except our t-shirts, so we're trying to remove 'media mail' from the shipping options if a t-shirt is in the cart.

I'm not a ruby expert but here is the code so far:

Input.cart.line_items.each do |item|
 if item.sku.upcase.include?("MS-SHIRT") || item.sku.upcase.include?("MS-TS")
  Output.shipping_rates = Input.shipping_rates.delete_if do |shipping_rate|
   shipping_rate.name.upcase.include?("MEDIA MAIL")
  end
 end
end

Output.shipping_rates = Input.shipping_rates

It is throwing this error:

[Error] undefined method 'sku' for #<Variant:0x7f7eb251fa20>
Hide media mail shipping rates:2:in Object.call
shopify/std_lib/core/list.rb:41:in List.each
Hide media mail shipping rates:1

sku appears to be correct for line items from the documentation that I've seen.  Any help as to what's wrong with this code would be greatly appreciated.  

[FaithCoder · Accepted solution]

This code is working. Just have to set all shirts as product type 'Clothing':

def cartHasShirt?
 for item in Input.cart.line_items
  product = item.variant.product
   if product.product_type.upcase.include?("CLOTHING")
    return true
   end
 end
 return false
end

if cartHasShirt?
 Output.shipping_rates = Input.shipping_rates.delete_if do |shipping_rate|
  shipping_rate.name.upcase.include?("MEDIA MAIL")
 end
end

Output.shipping_rates = Input.shipping_rates