title: "no implicit conversion of Symbol into String" when trying to create a new record
body: <p>I get the error <code>no implicit conversion of Symbol into String</code> when I try to create a new record, which I don't understand because all data is formed of strings.</p>
  
  <p>In the controller I have:</p>
  
  <pre><code>def new
      @account = Account.new
  end
  
  def create
      @account = Account.new(account_params)
      if @account.save
        redirect_to(:action =&gt; 'index')
      else
        render('new')
      end
  end
  
  private
      def account_params
      params.require(:account).permit(:username, :firstname, :lastname, :organisation, :phonenumber, :avatar, :about, :verified)
  end
  </code></pre>
  
  <p>And the form is simply:</p>
  
  <pre><code>&lt;%= form_for(@account) do |f| %&gt;
    &lt;div&gt;
     &lt;%= f.label :username %&gt;&lt;br&gt;
     &lt;%= f.text_field :username %&gt;
    &lt;/div&gt;
    &lt;div&gt;
     &lt;%= f.label :firstname %&gt;&lt;br&gt;
     &lt;%= f.text_field :firstname %&gt;
    &lt;/div&gt;
    &lt;div&gt;
     &lt;%= f.label :lastname %&gt;&lt;br&gt;
     &lt;%= f.text_field :lastname %&gt;
    &lt;/div&gt;
    ... more of the same...
  
    &lt;div class="actions"&gt;
      &lt;%= f.submit %&gt;
    &lt;/div&gt;
  &lt;% end %&gt;
  </code></pre>
  
  <p>And the migration file:</p>
  
  <pre><code>class CreateAccounts &lt; ActiveRecord::Migration
    def change
      create_table :accounts do |t|
  
        t.string   :username
        t.string   :firstname
        t.string   :lastname
        t.string   :organisation
        ...more of the same, all strings...
      end
    add_index :accounts, :username,                unique: true
    end
  end
  </code></pre>
  
  <p>I'm using Rails 3.2 and Ruby 2.1.5.</p>