DataDefinitionInterface:;getConstraint promises that it will only return array. However, FieldConfigBase::getConstraint and DataDefinition::getConstraint actually return array|null, violating the inteface.
Change the interface's documented return type to array|null to match the reality of Drupal (it seems like the lesser breaking change).
Active
11.0 🔥
Moving to 11.x as per https://www.drupal.org/about/core/blog/new-drupal-core-branching-scheme-... → . If this can only be done in a major version, then a [11.x] title prefix should be added and a "Major version only" tag too.