undefined method `merge' for 35:Fixnum - ruby-on-rails

Question

Found it
Don't use <%= f.hidden_field :field, number %> , use <%= f.hidden_field :field, value: number %>
Issue below
An ActionView::Template::Error occurred in bookings#new:
undefined method `merge' for 35:Fixnum
app/views/bookings/_form.html.erb:31:in `block in _app_views_bookings__form_html_erb__2731573742378725623_70113682151640'
Getting this horrible general error from our production website, and it's not clear why. It's not happening on our local hosts. Here's the line referenced above:
<%= current_employer.locations.first.name_or_address_1 %>
where name_or_address_1 is:
return "from #{name}" if name.present?
"from #{address_1}"
I've gone into the console and run "name_or_address_1" for every location in our database, which works fine, and "locations.first.name_or_address_1" for every employer in our database. Again, works fine. So surely it can't be this line?
Edit: I just commented out the line, deployed to production, and the error still occurs. What's going on? Why is the wrong line being referenced?
Here's the partial:
<%= form_for #employer, url: bookings_path, method: :post, html: { class: "main-form", id: "create-booking" } do |f| -%>
<% #employer.errors.full_messages.each do |msg| %>
<p><%= msg %></p>
<% end %>
<div id="bookings">
<ol class="numbers">
<li>
<legend>Location, Pay, & Vehicle</legend>
<div class="form-group">
<div class="row">
<div class="col-sm-6">
<label>Type of job</label><br>
<%= f.select(:job_type_id, options_from_collection_for_select(JobType.all, :id, :name_with_delivery), {}, { id: 'job-type', class: 'form-control' }) %>
</div>
<div class="col-sm-6">
<label>Vehicle needed</label><br>
<%= f.select(:vehicle_id, options_from_collection_for_select(Vehicle.all, :id, :name), {}, { id: 'vehicle-type', class: 'form-control' }) %>
</div>
</div>
</div>
<div class="form-group">
<div class="row">
<div class="col-sm-6">
<label>Location</label>
<% if current_employer.locations.size > 1 %>
<%= f.select :location_id, options_from_collection_for_select(current_employer.locations.all, :id, :name_or_address_1), {}, { class: 'form-control' } %>
<% elsif current_employer.locations.size == 1 %>
<p><strong>Location: </strong><%#= current_employer.locations.first.name_or_address_1 %></p>
<%= f.hidden_field :location_id, current_employer.locations.first.id %>
<% end %>
<%= link_to "or add new location", new_employer_location_path(current_employer, Location.new) %>
</div>
<div class="col-sm-6">
<%= f.label :pay %>
<span id="length-message" class="pull-right" style="color: #a94442"></span>
<br>
<%= f.text_field :pay, class: 'form-control', id: 'pay', maxlength: '18' %>
</div>
</div>
</div>
</li>
<legend>Shifts</legend>
<%= render 'booking', booking: Booking.new %>
</ol>
</div>
<%= link_to "Add another shift", "javascript:;", class: 'add-shift', style: 'margin-left: 40px;' %>
<script type="text/javascript">
$(".add-shift").click(function(){
$("ol.numbers").append("<%= j render 'booking', booking: Booking.new %>")
});
</script>
<%= f.submit "Post Shifts", class: 'btn green-button pull-right' %>
<br>
<br>
<br>
<span class="error-message bg-danger pull-right">
</span>
<% end %>

Answer 1

Don't use
<%= f.hidden_field :field, number %>
use
<%= f.hidden_field :field, value: number %>