title: NoMethodError: undefined method `to_d' for nil:NilClass
body: <pre><code>NoMethodError: undefined method `to_d' for nil:NilClass 
  </code></pre>
  
  <p>this seems to be inconsistent with other "to_"</p>
  
  <p>eg with Rails 3.2.14, and ruby 1.9.3p362:</p>
  
  <pre><code>1.9.3p362 :055 &gt; nil.to_f
   =&gt; 0.0 
  1.9.3p362 :056 &gt; nil.to_d
  NoMethodError: undefined method `to_d' for nil:NilClass
  1.9.3p362 :057 &gt; nil.to_s
   =&gt; "" 
  1.9.3p362 :058 &gt; nil.to_i
   =&gt; 0 
  </code></pre>
  
  <p>it means that when ever i might want to convert to big decimal that i first have to make sure the value is not nil and assign it a 0 value anyway... so... comments on what is the best way to make this consistent? and should i consider this a bug?</p>