The following code will generate a ClassCastException instead of a JspException:
   <%
      pageContext.setAttribute("invalidDataSource", new Integer("-1"));
   %>
     <sql:query var="resultSet"
                 dataSource= "${invalidDataSource}" >
         <c:out value="${sqlProps.Select_Jstl_Tab1_By_Id_Query}" />
      </sql:query>


Using the same code above, a NullPointerException will be generated if I change 
the dataSource attribute to:
dataSource= "${invalidDatasource}"