resetValue in custom UIInput Composite Component not working - jsf-2

Question

I have a custom UIInput wrapped in a composite component like this:
<cc:interface componentType="SingleUpload">
<cc:attribute name="value" required="true" />
...
</cc:interface>
<cc:implementation>
...
<p:fileUpload id="fileUpload" update="#form" auto="true"
fileUploadListener="#{cc.fileUploaded}" rendered="#{cc.attrs.value == null}"/>
...
<h:commandButton rendered="#{cc.attrs.value != null}" action="#{cc.removeFile}">
<p:ajax execute="#this" update="#form" />
</h:commandButton>
...
</cc:implementation>
The backing component looks like this:
#FacesComponent(value = "SingleUpload")
public class SingleUpload extends UIInput implements NamingContainer, Serializable {
/** */
private static final long serialVersionUID = 2656683544308862007L;
#Override
public String getFamily() {
return "javax.faces.NamingContainer";
}
public void fileUploaded(FileUploadEvent event) throws IOException {
FileData file = new FileData();
file.setContentMimeType(MimeTypeUtils.getContentType(event.getFile().getContentType(), event.getFile().getFileName()));
file.setInputStream(event.getFile().getInputstream());
file.setName(FilenameUtils.getName(event.getFile().getFileName()));
setValue(file);
}
public void removeFile() {
resetValue();
// value should be null now, but it is not, why??
FileData value=(FileData) getValue();
}
}
It is used this way:
<ki:singleUpload value="#{fileModel.file}" title="File Upload" />
So when the action removeFile is called, i want to set the value to null. This works, when I follow these steps:
load a page containing a singleUpload component with no initial value (fileModel.file == null)
upload a file, so value in SingleUpload is not null anymore
remove the file
But when I do the following
load a page containing a singleUpload component with an initial value (fileModel.file != null)
remove the intial value (click on button, removeFile is called)
=> removing the value from the component does not seem to be possible. Why??