Missing default length on ID field type string

[bigfoot90]

BC Break Report

Q	A
BC Break	yes
Version	3.1.0

Summary

Migrating from 2.19.2 to 3.1.0 I'm getting an error running schema:diff
Error:

In InvalidColumnDeclaration.php line 17:
  Column "site_name" has invalid type  
                                       
In ColumnLengthRequired.php line 26:
  Doctrine\DBAL\Platforms\MariaDB1060Platform requires the length of a VARCHAR column to be specified  

Previous behavior

Mapping before migration:

    <entity name="Domain\Model\Entity\Site">
        <id name="name" type="string"/>
        <field name="token" unique="true"/>
    </entity>

Current behavior

Actual mapping:

    <entity name="Domain\Model\Entity\Site">
        <id name="name" type="string" length="255"/>
        <field name="token" unique="true"/>
    </entity>

Expected behavior

Be able to migrate schema without errors and don't see changes on column name length.

How to reproduce

Create an entity with Id type string.
Value 255 was the default length for type string in ORM 2.19