Within the forEach loop you can write,
<c:choose>
<c:when test='${iterator.name eq ''}'>
<td style='background-color:red;'> <c:outvalue="${iterator.name}"/> </td>
</c:when>
<c:otherwise>
<td> <c:outvalue="${iterator.name}"/> </td>
</c:otherwise>
</c:choose>
As you can see when the value will be null you can set the background color of that cell to red and when it returns some value you can display it the way you were doing it before.