Laravel required_unless validation

I have an problem using required_unless validation.

What I want to do is say that building name is required when building number is empty or other way round so building number is required when building name is empty. At the moment it requires both.

public function rules(Request $request)
{
    $id = $request->input('entity_id');
    $entity = Entity::with('address')
        ->find($id);
    $validation = $entity->id;
    return [
        'name' => 'required|alpha_special|unique:entities,name,'.$validation.'|min:3|max:30',
        'type' => 'required',
        'email' => 'required|email|unique:entities,email,'.$validation,
        'building_name' => 'alpha|required_unless:building_number,value',
        'building_number' => 'numeric|required_unless:building_name,value',
        'street' => 'required|alpha_spaces',
        'town' => 'nullable|alpha',
        'city' => 'nullable|alpha',
        'postcode' => 'required|max:8',
        'telephone' => 'required|telephone',
        'ical' => 'nullable|active_url',
    ];
}

view:

<div class="hidden multi form-group{{ $errors->has('building_name') ? ' has-error' : '' }}">
                          <div class="building_name_message form-control alert-warning" style="display: none;"></div>
                            <label  id="building_name_label" for="building_name" >Building Name</label>
                            <input  id="building_name" type="text" class="form-field form-control" placeholder="Building name (If applicable)" name="building_name" value="{{ old('building_name') }}">
                              @if ($errors->has('building_name'))
                                <span class="help-block">
                                  <strong>{{ $errors->first('building_name') }}</strong>
                                </span>
                              @endif
                          <div class="building_number_message form-control alert-warning" style="display: none;"></div>
                            <label  id="building_number_label" for="building_number" >Building Number</label>
                            <input  id="building_number" type="text" class="form-field form-control" placeholder="Building Number (If applicable)" name="building_number" value="{{ old('building_number') }}">
                              @if ($errors->has('building_number'))
                                <span class="help-block">
                                  <strong>{{ $errors->first('building_number') }}</strong>
                                </span>
                              @endif
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                              </div>
                        </div>