Merge two relationships returns 'Method addEagerConstraints does not exist'

Im getting this error:

BadMethodCallException in Macroable.php line 81: Method addEagerConstraints does not exist.

In my User model im tryng to merge two relationships.

I have the same thing working on a different project but i can't figure out why here it isn't working.

public function stories()
{
return $this->hasMany('App\Models\Story')->where('published','=','1')->orderBy('order');
}

public function photos()
{
return $this->hasMany('App\Models\Photo')->where('published','=','1')->orderBy('order');
}

public function content()
{
return $this->stories->union($this->photos);
}

Version: Laravel 5.2.*

Does anyone had the same error o has any clue why it happens... i've been debugging for a while without any clues

Thanks in advance :)