grails paginate turning maps into strings - grails

Question

I am trying to create a search action in my grails app that accepts a number of criteria and displays a table (similar to a default index action) of instances that match the criteria.
For search criteria that have many results I would like to use the paginate tag:
<g:paginate total="${alarmInstanceCount ?: 0}" />
By default, this tag forgets the search criteria. I believe that the params attribute allows me to add the search parameters to the links that the paginate tag creates.
To encapsulate my search criteria, I've organized them into their own map called searchParams.
However, when I try to pass my searchParams to the paginate tag:
<g:paginate total="${alarmInstanceCount ?: 0}" params="${[searchParams:searchParams]}"/>
my searchParams are turned into a string.
Here is an example of what I mean.
When I first open the search page the controller reports the params as follows:
[action:index, format:null, controller:alarm, max:10]
null
class org.codehaus.groovy.runtime.NullObject
So, since the params map doesn't contain an entry for searchParams it comes up as null and has the NullObject class. My code handles this case gracefully.
When I enter some text into the channelName field the controller reports the params as follows:
[searchParams.channelName:SWR, searchParams:[channelName:SWR], _action_index:List, _method:PUT, action:index, format:null, controller:alarm, max:10]
[channelName:SWR]
class org.codehaus.groovy.grails.web.servlet.mvc.GrailsParameterMap
So, now the params map has a searchParams entry which refers to a GrailsParameterMap. This is the desired behaviour, and the controller interprets this correctly.
However, if I click on the first entry in the paginate bar, the controller reports the params as follows:
[max:10, searchParams:[channelName:SWR], offset:10, action:index, format:null, controller:alarm]
[channelName:SWR]
class java.lang.String
In this third case, the params map has a searchParams entry that looks correct, but is actually a String object. This causes my code to implode with a:
No such property: channelName for class: java.lang.String.
Is this the expected behaviour of the params attribute of the paginate tag? If so, what is the cleanest way for me to achieve the behaviour I am looking for (i.e. searchParams being passed as a map and not a string to my controller)?
Edit:
Here is the relevant gsp code for my search form:
<g:form url="[action:'index']" method="PUT" >
<fieldset class="form">
<div class="fieldcontain">
<label for="channelName">
<g:message code="alarm.channelName.label" default="Channel Name" />
</label>
<g:textField name="searchParams.channelName" value="${searchParams?.channelName}"/>
</div>
</fieldset>
<fieldset class="buttons">
<g:actionSubmit class="list" action="index" value="${message(code: 'default.button.list.label', default: 'List', args: [entityName])}" />
</fieldset>
</g:form>
and here is my index action:
def index(Integer max) {
params.max = Math.min(max ?: 10, 100)
def alarmCriteria = new DetachedCriteria(Alarm)
def channelInterfaceInstances = ChannelInterface.list();
if(params.searchParams?.channelName != null && params.searchParams?.channelName != "" && params.searchParams?.channelName != []) {
alarmCriteria = alarmCriteria.and {
like("channelName", "%${params.searchParams?.channelName}%")
}
}
def results = alarmCriteria.list(params) {}
respond results, model:[alarmInstanceCount: results.totalCount, searchParams: params.searchParams]
}