Issue with nested TextColumn on Polymorphic relation

Hi folks, I try to display a TextColumn with a nested relation inside. With a simple relation like :

public function assignee() {
        return $this->belongsTo(User::class);
    }

public function assignee() {
        return $this->belongsTo(User::class);
    }

public function assignee() {
        return $this->belongsTo(User::class);
    }

public function assignee() {
        return $this->belongsTo(User::class);
    }

...

Tables\Columns\TextColumn::make('assignee.initials')

Tables\Columns\TextColumn::make('assignee.initials')

Tables\Columns\TextColumn::make('assignee.initials')

Tables\Columns\TextColumn::make('assignee.initials')

It works ! but when the relation is polymorphic :

public function owner() {
        return $this->morphTo('ownerable');
    }

public function owner() {
        return $this->morphTo('ownerable');
    }

public function owner() {
        return $this->morphTo('ownerable');
    }

public function owner() {
        return $this->morphTo('ownerable');
    }

Tables\Columns\TextColumn::make('owner')

Tables\Columns\TextColumn::make('owner')

Tables\Columns\TextColumn::make('owner')

Tables\Columns\TextColumn::make('owner') will display the owner object and it's ok but

Tables\Columns\TextColumn::make('owner.initials')

Tables\Columns\TextColumn::make('owner.initials')

Tables\Columns\TextColumn::make('owner.initials')

Tables\Columns\TextColumn::make('owner.initials') will result in empty cells. Someone can give me some help ?