[TYPO3-mvc] Error using link.action, while form.submit works

[Michael Oehlhof]

Hello.

I have a problem with a generated action link.

In my extension there is an individual search mask.
The data from the search mask is transfered via a demand object to the 
find action, where the data is displayed in list form.
	Tx_Myext_Domain_Model_Demand extends
		Tx_Extbase_DomainObject_AbstractValueObject

For scrolling in the result set I need a link to show the previous (or 
the next) couple of items (same action, same view, different offset).

The link I try to use is following:
<f:link.action action="find"
	arguments="{demand: demand, count: count, offset: prev}">
prev
</f:link.action>

But this results infollowing error:
Uncaught TYPO3 Exception
#1251730701: The value must be of type "Tx_Myext_Domain_Model_Demand", 
but was of type "NULL".

Whe I use a form with an submit button it works:
<f:form class="tx_myext_searchform" method="post" action="find"
	name="demand" object="{demand}"
	arguments="{count: count, offset: prev}" >
     <f:form.hidden id="searchTitle" property="searchTitle" />
     <f:form.hidden id="searchCountries" property="searchCountries" />
     <f:form.submit name="submitButton" id="prevButton" value="prev" />
</f:form>

What I am doing wrong with the link generation?

Any hint is welcome.

Regards
Michael