cannot check box in form:checkboxes

[geek.shrek]

Hi,

I have form:checkboxes that the data came from referenceData.
I can retrieve the data but when I select one of the checkboxes and click submit, the form doesn't go to "protected ModelAndView onSubmit(HttpServletRequest request,
HttpServletResponse response, Object command,BindException errors)" method

But when I didn't select any of the checkboxes it goes to "onSubmit" method but having nullpointerexception

Here's my jsp

<form:form commandName=""test_command" method="post" action="custom.htm"  id="bookID">
		<table class="Style3">
		<tr>
		<td>Delete</td>
		</tr>
		<tr>
		<td>
			<form:checkboxes path="deletedBooks" items="${books}"  cssClass="note" element="checkbox"  delimiter="<br/>"  />
		</td>
		</tr>
		<tr>
			<td><input type="submit" name="submit" title="Delete Selected"/></td>
		</tr>	
		</table>
	</form:form>

My bean config

  	<bean id="bookCustom" class="com.test.BookController">
    	<property name="formView" value="custom"/>
    	<property name="commandName" value="test_command"/>
    	<property name="successView" value="custom"/>
    	<property name="commandClass" value="com.test.BookDao"/>
  	</bean>

my BookDao

private Map<String,String> deletedBooks;

//get and setters

Can someone point me what did I do wrong with my checkboxes?

Thanks,