NullPointerException in table

[Phantess]

I'm using JavaFX 8. Right now I keep getting a NullPointerException for my tables. I have initalized the data and it appears when I click on the button to bring it up. However, when I try to search or delete something from the table it keeps giving me the exception. I've sifted through my code and double checked, but I cannot figure out why. It is only happening in my Modify Products.

Here are my code snippets.

MainApp.java

    private final ObservableList<Part> PartsData = FXCollections.observableArrayList();
    private final ObservableList<Product> ProductsData = FXCollections.observableArrayList();

    public MainApp() {
        PartsData.add(new Inhouse("Part 1", 1,1.99,10, "", 9874));
        PartsData.add(new Inhouse("Part 2", 2,1.99,10, "", 1234));
        PartsData.add(new Outsourced("Part 3", 3,1.99,10));
        PartsData.add(new Outsourced("Part 4", 4,1.99,10));
        ProductsData.add(new Product(1,"Product 1",3,2.99, PartsData.get(0)));
        ProductsData.add(new Product(2,"Product 2",3,2.99, PartsData.get(1)));
        ProductsData.add(new Product(3,"Product 3",3,2.99, PartsData.get(2)));
        ProductsData.add(new Product(4,"Product 4",3,2.99, PartsData.get(3)));
    }

    public ObservableList<Part> getPartsData(){
    return PartsData;
}

public ObservableList<Product> getProductsData(){
    return ProductsData;
}

public boolean showModifyProducts(Product products) {
    try {
        FXMLLoader loader = new FXMLLoader();
        loader.setLocation(MainApp.class.getResource("view/modProduct.fxml"));
        AnchorPane page = (AnchorPane) loader.load();

        Stage dialogStage = new Stage();
        dialogStage.setTitle("Modify Product");
        dialogStage.initModality(Modality.WINDOW_MODAL);
        dialogStage.initOwner(primaryStage);
        Scene scene = new Scene(page);
        dialogStage.setScene(scene);

        ModProductController controller2 = loader.getController();
        controller2.setPartsTable(PartsData);
        controller2.setDialogStage(dialogStage);
        controller2.setProduct(products);

        dialogStage.showAndWait();

        return controller2.isOkClicked();
    } catch (IOException e) {
        e.printStackTrace();
        return false;
    }
}

ModProductController.java

    @FXML
    private void initialize(){
        partIDColumn.setCellValueFactory(cellData -> cellData.getValue().partIDProperty().asObject());
        partNameColumn.setCellValueFactory(cellData -> cellData.getValue().partNameProperty());
        partInvColumn.setCellValueFactory(cellData -> cellData.getValue().instockProperty().asObject());
        partCostColumn.setCellValueFactory(cellData -> cellData.getValue().priceProperty().asObject());

        ApartIDColumn.setCellValueFactory(cellData -> cellData.getValue().partIDProperty().asObject());
        ApartNameColumn.setCellValueFactory(cellData -> cellData.getValue().partNameProperty());
        ApartInvColumn.setCellValueFactory(cellData -> cellData.getValue().instockProperty().asObject());
        ApartCostColumn.setCellValueFactory(cellData -> cellData.getValue().priceProperty().asObject());
        grpProduct = new Product();
    }

    public void setPartsTable(List<Part> parts) {
        partsTable.getItems().setAll(parts);
}

    public void setProduct(Product product) {
        this.grpProduct = product;
        modProductIdTxt.setText(Integer.toString(product.getProductID()));
        modProductName.setText(product.getProductName());
        modProductInv.setText(Integer.toString(product.getProductInv()));
        modProductPrice.setText(Double.toString(product.getProductPrice()));
        modProductMin.setText(Integer.toString(product.getProductMin()));
        modProductMax.setText(Integer.toString(product.getProductMax()));
        ApartsTable.setItems(product.getlist());
    }

    @FXML
    private void removePart() {
        Part selectedPart = ApartsTable.getSelectionModel().getSelectedItem();

        if (selectedPart != null) {
            mainApp.getPartsData().add(selectedPart); //Line 144

            Alert alert = new Alert(Alert.AlertType.CONFIRMATION);
            alert.setTitle("Confirm Delete");
            alert.setContentText("Do you want to delete " + selectedPart.getPartName() + "?");
            alert.showAndWait()

                    .filter(response -> response == ButtonType.OK)
                    .ifPresent(response -> grpProduct.getlist().remove(selectedPart));
            ApartsTable.setItems(grpProduct.getlist());

        }
    }

    @FXML
    public void searchApart() {
        String searchAparts = modApartsTableSearch.getText();
        FilteredList<Part> searchText = searchApart(searchAparts); //Line 287
        SortedList<Part> sortedData = new SortedList<>(searchText);
        sortedData.comparatorProperty().bind(ApartsTable.comparatorProperty());
        ApartsTable.setItems(sortedData);
    }

    public FilteredList<Part> searchApart(String s) {
        return mainApp.getPartsData().filtered(p -> p.getPartName().toLowerCase().contains(s.toLowerCase())); //Line 294
    }

This pops up in my Output.

Caused by: java.lang.NullPointerException
at inventory.view.ModProductController.removePart(ModProductController.java:144)
at inventory.view.ModProductController.searchApart(ModProductController.java:294)
at inventory.view.ModProductController.searchApart(ModProductController.java:287)

I hope I got all the relevant code. Any help will be appreciated! Thanks!

[JamesCherrill]

mainApp.getPartsData().add(selectedPart);

If that line throws an NPE then either mainApp is null getPartsData is returning null.
A quick print (or use a debugger) wil quickly show which and thus show you where to look next.

One could also ask why a method called "search" is calling a method called"remove". Search is not normally destructive!