NameError in Users#new

Showing users/_address.html.erb where line #4 raised:

`@user[address_attributes][]' is not allowed as an instance variable name

Extracted source (around line #4):

1: <div class="address">
2: <hr />
3: <% fields_for "user[address_attributes][]", address do |a| %>
4:   <%= a.error_messages %>
5:
6:   <p>
7:     <%= a.label :address1 %><br />

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The partial is called like this:

<%= render :partial => 'address', :locals => {:user => @user} %>

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In the User model, address_attributes is defined as a virtual attribute:

  def address_attributes=(address_attributes)
    logger.info "=====> inside address_attributes"
    address.build(address_attributes)
  end