title: 'null' is shown in Angular UI Bootstrap's datepicker input field on Internet Explorer 9
body: <p>I'm using Angular UI Datepicker. It's behavior is correct on all tested browsers except IE9. On IE9 when i choose some date, then open datepicker again and click on "Clear" button(native button coming from the directive) then "null" text is shown in datepicker's input field. </p>
  
  <p><a href="https://i.stack.imgur.com/TFSne.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/TFSne.png" alt="enter image description here"></a></p>
  
  <p><a href="https://i.stack.imgur.com/ZV0Si.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ZV0Si.png" alt="enter image description here"></a></p>
  
  <p>I have found a related <a href="https://stackoverflow.com/questions/5387038/null-values-shown-in-form-fields-in-ie">question</a> about that issue. The problem is that in IE whenever javascript sets the input value to a variable which is null then the input field is filled up with the text "null". So the solution for IE9 is to do </p>
  
  <pre><code>document.getElementById('some_id').value = someVar || ''
  </code></pre>
  
  <p>instead of</p>
  
  <pre><code>    document.getElementById('some_id').value = someVar;
  </code></pre>
  
  <p>but that solution is not applicable for my case because the value of input is being set in the code of directive and i don't want to change that code because dependency is coming from bower and can be updated in future. 
  The only thing i can do is to write an angular watcher for datepicker model value setting it to empty string in case when it's value becomes null or undefined, but i don't like that solution as i need to do that for each and every page where datepicker is used.</p>
  
  <p>Any idea ? </p>