[PHP 8.5] Warning with dynamic_entity_reference fields

Problem/Motivation

This surfaced after migrating a project to PHP 8.5 on Dynamic Entity Reference fields . Suddenly I've noticed this error message:

Deprecated function: Using null as an array offset is deprecated, use an empty string instead in Drupal\token\TokenEntityMapper->getTokenTypeForEntityType() (line 72 of modules/contrib/token/src/TokenEntityMapper.php)

Tracking the error I see it happens in \Drupal\token\Hook\TokenTokenInfoHooks::fieldTokenInfoAlter(), lines ~693-694

$referenced_entity_type = $property_definition->getTargetDefinition()->getEntityTypeId();
$referenced_token_type = $this->tokenEntityMapper->getTokenTypeForEntityType($referenced_entity_type);

The problem seems to be that $referenced_entity_type is computed to NULL. But the Dynamic Entity Reference field is a special kind of fish. Even it extends EntityReferenceItem the 'entity' field property doesn't set a target entity data definition because the target entity type is unknown and is assigned dynamically (see \Drupal\dynamic_entity_reference\Plugin\DataType\DynamicEntityReference).

Steps to reproduce

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Proposed resolution

Only create the token if $referenced_entity_type is not NULL.

Remaining tasks

None.

User interface changes

None.

API changes

None.

Data model changes

None.