Params is playing with me?

Demo.groovy

class Category {

  String name
	
	String description
	
	Category parent
	
	static hasMany = [subcategories : Category]
	
	static mappedBy = [children: 'parent']
	
	static constraints = {
		name blank: false, maxSize: 30
		description blank: false, maxSize: 100
		parent nullable: true
	}
	
	static mapping = {
		subcategories sort: "id"
	}
	
	static Category getRoot() {
		def cat = Category.executeQuery(" from Category where parent is null ")
		return cat ? cat[0] : null
	}
	
	boolean isLeaf() {
		return subcategories ? (subcategories.size() > 0 ? false : true) : true
	}
	
	@Override
	public String toString() {
		"[category: $name, description: $description, leaf: ${isLeaf()}]"
	}
	
}


class CategoryController extends RestfulController<Category> {
  
	//def categoryService
	
	static responseFormats = ['json']
	
	CategoryController() {
		super(Category)
	}
	
	@Override
	protected Category createResource(Map params) {
		Category instance = super.createResource(params);
		println "params: $params"
		if(params.parent?.id) {
			instance.parent = Category.get(params.parent.id)
		}
		
		return instance
	}
	
	
	@Override
	protected Map getParametersToBind() {
		println "PARAMS II: $params"
		return super.getParametersToBind();
	}
	
	//def tree() {
	//	render (categoryService.getCategoryTree() as JSON)
	//}
	
}


class UrlMappings {

  static mappings = {
        "/$controller/$action?/$id?(.${format})?"{
            constraints {
                // apply constraints here
            }
        }

		"/category/tree" (controller: "category", action: "tree")
		
		"/category"(resources: "category")
		
    "/"(controller: 'app', action: 'redir')
		
    "500"(view:'/error')
	}
}