title: Empty array value being input with simple_form entries
body: <p>I'm still new to rails and simple_form and have been trying to implement a multiple select option to give a user multiple roles.</p>
  
  <p>Current input looks like this</p>
  
  <pre><code>&lt;%= f.input :secondary_role, :collection =&gt; UseridRole::VALUES, :include_blank =&gt; false,:label =&gt; "Secondary Role(s):", :input_html =&gt; {  :class =&gt; " simple_form_bgcolour simple_form_position overide_selection_field_width", :size =&gt; 4, multiple: true } %&gt;
  </code></pre>
  
  <p>So, this does work, but is including an empty value at the start of my array:</p>
  
  <pre><code>"secondary_role" : [
          "",
          "admin"
      ]
  </code></pre>
  
  <p>I have the same code above which works for my primary_role value which is a string, but my secondary_role can have multiple values so is stored as an array.  </p>
  
  <p>Where should I be looking to fix this issue?</p>