Validation of unique value fails when updating record

I created a new field on the customer form in the admin. I did so, with an EAV attribute like this inside the InstallData:

\$customerSetup->addAttribute(Customer::ENTITY, self::DOCUMENT_NUMBER, [
'type' => 'varchar',
'label' => 'Document Number',
'input' => 'text',
'required' => true,
'visible' => true,
'user_defined' => true,
'searchable' => true,
'visible_on_front' => true,
'unique' => true,
'sort_order' => 31,
'position' => 31,
'system' => 0,
]);


It worked and I can see and save data using the customer form. The problem is that whenever I try to edit a costumer, it throws an error saying: The value of attribute "Document Number" must be unique. This would make sense if I were trying to create a new customer with an already used 'Document Number' but since I'm doing an updated on an existing record it should not give me this error.

Am I missing some configuration? Thanks.