Global Add-ons: random behaviour updating options

[DenisFrezzato]

What I expected

After updating the options of a global add-on, I expect the options correctly saved.

What happened instead

Saved options is different from the options I checked/unchecked. Furthermore, when saving, I get this notice:
Notice: Undefined index: product-type in /[...]/wp-content/plugins/woocommerce-accommodation-bookings/includes/integrations/class-wc-accommodation-booking-addons.php on line 66

Steps to reproduce the issue

Here a few examples.
Starting state:

• Bookings: Multiply cost by person count
• Bookings: Multiply cost by person count
• Bookings: Multiply cost by block count
• Bookings: Multiply cost by number of nights

Updating with these options:

• Bookings: Multiply cost by person count
• Bookings: Multiply cost by person count
• Bookings: Multiply cost by block count
• Bookings: Multiply cost by number of nights

I get this:

• Bookings: Multiply cost by person count
• Bookings: Multiply cost by person count
• Bookings: Multiply cost by block count
• Bookings: Multiply cost by number of nights

Updating with these options:

• Bookings: Multiply cost by person count
• Bookings: Multiply cost by person count
• Bookings: Multiply cost by block count
• Bookings: Multiply cost by number of nights

I get this:

• Bookings: Multiply cost by person count
• Bookings: Multiply cost by person count
• Bookings: Multiply cost by block count
• Bookings: Multiply cost by number of nights

Updating with these options:

• Bookings: Multiply cost by person count
• Bookings: Multiply cost by person count
• Bookings: Multiply cost by block count
• Bookings: Multiply cost by number of nights

I get this:

• Bookings: Multiply cost by person count
• Bookings: Multiply cost by person count
• Bookings: Multiply cost by block count
• Bookings: Multiply cost by number of nights

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