title: Rails: money gem converts all amounts to zero
body: <p>I'm trying to use the <a href="https://github.com/RubyMoney/money" rel="noreferrer">money gem</a> to handle currency in my app but I'm running into a strange error. This is what I have in my "record" model:</p>
  
  <pre><code>composed_of :amount,
              :class_name =&gt; "Money",
              :mapping =&gt; [%w(cents cents), %w(currency currency_as_string)],
              :constructor =&gt; Proc.new { |cents, currency| Money.new(cents || 0, currency || Money.default_currency) },
              :converter =&gt; Proc.new { |value| value.respond_to?(:to_money) ? value.to_money : raise(ArgumentError, "Can't convert #{value.class} to Money") }
  </code></pre>
  
  <p>amount is an integer. </p>
  
  <p>When I create a new record it ignores whatever value I put in the amount field and defaults it to 0. Is there something I need to add to the forms?</p>
  
  <p>I'm using rails 3.0.3 and the money gem version is 3.5.5</p>