undefined method `+' for nil:NilClass - Ruby
<p>Currently I have a controller method that will increment 1 every time a user inputs there number in a view form. I'm going to show the code and the error I just want to make sure I'm giving enough background here. So, I have another form that creates a <code>subscriber</code> this model takes in name and phone number but it also has a visit attribute that is a int data type. So the controller method that is giving me the problem, it's function is to increment 1 visit to the Subscriber by finding the number attached to that Subscrier. But when the user types in their phone number it throws this error undefined method `+' for nil:NilClass and I truly and stumped on how to fix it. Here is my code for clarity.</p>

<p>CONTROLLER:</p>

<pre><code> def visit
  @subscriber = Subscriber.find_by_phone_number(params[:phone_number])
  if @subscriber
   @subscriber.visit += 1
   @subscriber.save
   flash[:notice] = flash[:notice] = "Thank You #{@subscriber.first_name}. You have #{@subscriber.days_till_expired} until renewal"
   redirect_to subscribers_search_path(:subscriber)
  else
   render "search"
  end
 end
</code></pre>

<p>ERROR:</p>

<p><a href="https://i.stack.imgur.com/HjfHs.png" rel="noreferrer"><img src="https://i.stack.imgur.com/HjfHs.png" alt="enter image description here"></a></p>

<p>I'm not sure what other code would be applicable? let me know if you need more info. Thank You.</p>