Custom View 'Does not Have'

Hi

I have created a view via the CRM SDK. Using the the following Fetch. Which is suppose to be. Leads which dont have a phone call.

System.String fetchXml =
@"<fetch mapping="logical" >

<entity name="lead" >
<attribute name="createdon" />
<attribute name="leadqualitycode" />
<attribute name="subject" />
<attribute name="fullname" />
<filter>
<condition attribute="statuscode" operator="eq" value="1" />
</filter>
<order attribute="createdon" descending="true" />
<link-entity name="phonecall" from="regardingobjectid" to="leadid" link-type="outer" >
<attribute name="subject" />
</link-entity>

<filter type="and" >
<condition attribute="regardingobjectid" operator="null" />
</filter>

</entity>

</fetch>";

This creates the view fine. However it is still returning the leads which do have a phone call.