Problems with tutorial: "Creating a Web Dynpro Tree"

Question

Hi!
I'm a rookie and therefore I'm practicing on compleating some tutorials like "Creating a Web Dynpro Tree" (https://www.sdn.sap.com/irj/sdn/go/portal/prtroot/docs/library/uuid/f0ec6622-8da5-2a10-349b-868b6a553efa)
I did just as the tutorial told me to (I think) but still I get a java.lang.NullPointerException when I deploy and run my application.
In the bold line is where it is something wrong:
public static void wdDoModifyView(IPrivateTreeView wdThis, IPrivateTreeView.IContextNode wdContext, com.sap.tc.webdynpro.progmodel.api.IWDView view, boolean firstTime)
    //@@begin wdDoModifyView
       if (firstTime) {
            IWDTreeNodeType treeNode = (IWDTreeNodeType) view.getElement("TreeNodeType");
            /* parameter mapping from parameter "path" to
parameter "selectedElement"
            treeNode._mappingOfOnAction()._addSourceMapping("path", "selectedElement");
            /* parameter mapping from parameter "path" to
parameter "element".
            treeNode._mappingOfOnLoadChildren()._addSourceMapping("path","element");
    //@@end
What I don't understand is what the function/meaning of the parameter path is. The parameters selectedElement and element I do recognize and have written. And I don't understand why there is a difference between the two underscored line of code (see above) even though the comments claim that it does the same kind of mapping.
Best regards
/Johan

Answer 1

I tried to get "addSourceMapping()." underscored so people would better understand what I was referring to but it didn't work and that's why it looked weired.
Thanks for your help Armin, now it works fine.
It was as you said.
if (firstTime) {
IWDTreeNodeType treeNode = (IWDTreeNodeType) view.getElement("TreeNodeType");
When I changed "TreeNodeType" to it's real ID, "TheNode" I didn't get a nullPointerException. I think it must be wrong in the tutorial because I followed the instructions which said to name it "TheNode" but then the author mus have forgot to change it from the default ID ("TreeNodeType").
Best Regards!
/Johan