Empty multiselect is not set
Having the following input:
<label for="cars">Make your choice:</label>
<select name="choice" id="choice" multiple>
<option value="Yes">Volvo</option>
<option value="No">Saab</option>
<option value="Maybe">Saab</option>
</select>
If nothing is selected, the name of the property is not sent to the server (e.g. if you expect the full set to be sent to the server)
A hack to fix this is to add a hidden property with the same name.
<input type="hidden" name="myitems" value="" />