SAPUI5 failed to load 'null/Page.js'

please take a look at my code. I get everytime the following error:

"failed to load 'null/Page.js' from https://sapui5.hana.ondemand.com/resources/null/Page.js: 0 - error

Here are the most important Code:

index.html

    var oModel = sap.ui.model.json.JSONModel();
    oModel.setData(oData);
    sap.ui.getCore().setModel(oModel);


    var oAppView = sap.ui.view("appview", {
        type: sap.ui.core.mvc.ViewType.XML,
        viewName: "sapui5.demo.mvcapp.view.App",
    });
    var oApp = oAppView.byId("app");
    oAppView.placeAt("content");

Master.Controller.js

sap.ui.define([
"sap/ui/core/mvc/Controller"
], function(Controller) {
    "use strict";
    return Controller.extend("sapui5.demo.mvcapp.controller.Master", {
        onListPress: function(oEvent) {
            var sPageId = "appview--detailPage";
            oApp.to(sPageId);

            var oPage = oApp.getPage(sPageId);
            var oContenxt = oEvent.getSource().getBindingContext();
            oPage.setBindingContext(oContenxt);
        }
    });

});

App.view.xml

<mvc:View xmlns:mvc="sap.ui.core.mvc" xmlns="sap.m">
<App id="app">
    <pages>
        <mvc:XMLView id="masterPage" viewName="sapui5.demo.mvcapp.view.Master" />
        <mvc:XMLView id="detailPage" viewName="sapui5.demo.mvcapp.view.Detail" />
    </pages>
</App>
</mvc:View>

Kind Regards Phillip