Boolean custom Field sending empty string when false.

[axyut]

Describe the bug
When trying to give false value for Boolean custom field it is sent as empty string.

To Reproduce
Steps to reproduce the behavior:

1. Create a new custom fields and set the type to Boolean. nullable being true was also tested.
   

2. Go to the customer tab (if custom fields pushed for customer) and uncheck to send the value as false.
   

3. Try to update Customer

4. See error
   

Expected behavior
Just sending the false value instead of empty string "" and customer is updated.

Environment (please complete the following information):

• "@vendure/core": "2.0.6",
• "pg": "8.11.0",
• "typescript": "4.9.5"
• node : 18.16.0