title: Rails - simple form - boolean attribute not accepting false/no radio button choice
body: <p>I am making a rails app using simple form (with bootstrap).</p>
  
  <p>I have this question in my form:</p>
  
  <pre><code>&lt;%= f.input :ethics, as: :radio_buttons, label: 'Is an ethics review relevant?' %&gt;
  </code></pre>
  
  <p>The ethics attribute is a boolean in my table.</p>
  
  <p>The form renders with radio buttons for yes/no. </p>
  
  <p>The default shows as no - but if that's the answer I want to give I'm stuck because I can't submit the form. I get an error that says an answer is required.</p>
  
  <p>Why doesn't simple form acknowledge false as a boolean answer?</p>
  
  <p>The log shows:</p>
  
  <pre><code>Processing by ProjectsController#create as HTML
    Parameters: {"utf8"=&gt;"✓", "authenticity_token"=&gt;"", "project"=&gt;{"title"=&gt;"asdfsdf ", "byline"=&gt;"", "description"=&gt;"asdfsdf ", "problem"=&gt;"", "solution"=&gt;"", "remark"=&gt;"",  "ethics"=&gt;"false", 
  </code></pre>