RoR - The record failed to save when after its foreign key was set to nil

I'm trying to solve this problem of mine. I'll tell you what I did, where I struggle and hopefully you can lend me a hand. I'm kinda new to this Rails thing and get hopefully 1-2 good tips regarding my problem. That would be really awesome.

Problem:

LocationsController request to edit should load the requested location
Failure/Error: @location.image = @image
     ActiveRecord::RecordNotSaved:
       Failed to remove the existing associated image. 
The record failed to save when after its foreign key was set to nil.

LocationsController request to edit should be successfull
Failure/Error: @location.image = @image
     ActiveRecord::RecordNotSaved:
       Failed to remove the existing associated image. 
The record failed to save when after its foreign key was set to nil.

Part of the Controller:

def new
 @location = Location.new
end

def create
  @location = Location.new(params[:location])
  @location.owner_id = current_user.id
  @address = Address.new(params[:address])
  @location.image = Image.new(params[:image])
  responds_to_parent do
    if @location.save && @location.image.update_from_uploaded_data(params[:image])
      @address.addressable = @location
      @address.save
      @locations = Location.all_as_select_options
      respond_to do |format|
        format.js { render layout: false }
      end
    else
      render :update
    end
  end
end

def edit
  @address = @location.address
end

def update
  @location.image ||= Image.new
  @location.address ||= Address.new
  address = params[:address]

  if @location.update_attributes(params[:location]) &&   @location.address.update_attributes(address) && @location.image.update_from_uploaded_data(params[:image])
    flash[:notice] = 'Daten für den Ort wurden geändert.'
    redirect_to location_path(@location)
  else
    flash[:notice] = 'Die Daten konnten nicht gespeichert werden'
    render action: 'edit'
  end
end

def destroy
  @location.destroy if @location.owner.id == current_user.id
  redirect_to action: 'index', controller: 'locations'
end

private

def load_location
  @location = Location.find(params[:id])
end

Rspec:

describe 'request to edit' do
      before do
        login(mock_admin)
        @location = create_location
        @image = create_image
        Location.stub!(:find).and_return(@location)
        Image.stub!(:find).and_return(@image)
        @location.image = @image
        get :edit, id: @location.id
      end
      it 'should be successfull' do
        response.should be_success
      end
      it 'should load the requested location' do
        assigns(:location).should eql(@location)
      end
      it 'should load the locations address' do
        assigns(:address).should eql(@location.address)
      end
    end

My attempt: Allowing parameters like location and image in my edit method. Like it was suggested at Can't update my nested model form for has_one association

I tried the

'params.require(:...).permit(...)'

and

accepts_nested_attributes_for(:..., update_only: true)

solution which were suggested. But even with all parameters allowing it didn't work out. Do you knowwhy though? I tried to modify the methods but o well...