your search form has a number of select list on it that dont have any values. for example:
<select name="S_BedRooms" id="S_BedRooms">
</select>
these are being caught by data assist search and treated as null. to have DataAssist search ignore them if a valueis not selected, you need to have a default empty option:
<select name="S_BedRooms" id="S_BedRooms">
<option ="">Make a selection</option>
</select>