Declaração do @FXML no Java FX

Olá pessoal, estou fazendo um exemplo simples de um programa que tem uma combobox, ao clicar nele os itens aparecem. Porém se não coloco no FXMLcontroller antes da declaração da combobox o parâmetro @FXML e seu pacote respectivo, ao executar o programa da um erro. Qual é a importância do @FXML, por que quando não declaro o programa da erro? Segue abaixo o erro exibido:

Exception in Application start method

java.lang.reflect.InvocationTargetException

at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)

at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

at java.lang.reflect.Method.invoke(Method.java:498)

at com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:389)

at com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:328)

at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)

at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

at java.lang.reflect.Method.invoke(Method.java:498)

at sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:767)

Caused by: java.lang.RuntimeException: Exception in Application start method

at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:917)

at com.sun.javafx.application.LauncherImpl.lambda$launchApplication$1(LauncherImpl.java:182)

at java.lang.Thread.run(Thread.java:748)

Caused by: javafx.fxml.LoadException:

file:/C:/Users/eder/Documents/NetBeansProjects/JavaFXBasico2/dist/run2041392979/JavaFXBasico2.jar!/javafxbasico2/FXMLComboBox.fxml

at javafx.fxml.FXMLLoader.constructLoadException(FXMLLoader.java:2601)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2579)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2441)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3214)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3175)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3148)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3124)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3104)
at javafx.fxml.FXMLLoader.load(FXMLLoader.java:3097)
at javafxbasico2.MainComboBox.start(MainComboBox.java:23)
at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$8(LauncherImpl.java:863)
at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$7(PlatformImpl.java:326)
at com.sun.javafx.application.PlatformImpl.lambda$null$5(PlatformImpl.java:295)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.application.PlatformImpl.lambda$runLater$6(PlatformImpl.java:294)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$3(WinApplication.java:177)
... 1 more

Caused by: java.lang.NullPointerException

at javafxbasico2.FXMLComboBoxController.carregarComboBox(FXMLComboBoxController.java:46)

at javafxbasico2.FXMLComboBoxController.initialize(FXMLComboBoxController.java:33)

at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2548)

… 17 more

Exception running application javafxbasico2.MainComboBox

Java Result: 1

Deleting directory C:\Users\eder\Documents\NetBeansProjects\JavaFXBasico2\dist\run2041392979