// espace réservé du code
public class TestListener implements Listener {
    @EventHandler(ignoreCancelled = true)
    public void onVehicleCreate(VehicleCreateEvent event) {

        if(event.getVehicle() instanceof InventoryHolder)
        {

            InventoryHolder vehicle = (InventoryHolder) event.getVehicle();
            @SuppressWarnings("unused")
            Boolean test = vehicle.getInventory().contains(Material.AIR);
            
        }
    }

}

// espace réservé du code
Caused by: java.lang.NullPointerException
        at org.bukkit.craftbukkit.v1_11_R1.inventory.CraftInventory.getContents(CraftInventory.java:66) ~[craftbukkit-1.11.2.jar:git-Bukkit-cb61ac0]
        at org.bukkit.craftbukkit.v1_11_R1.inventory.CraftInventory.getStorageContents(CraftInventory.java:54) ~[craftbukkit-1.11.2.jar:git-Bukkit-cb61ac0]
        at org.bukkit.craftbukkit.v1_11_R1.inventory.CraftInventory.contains(CraftInventory.java:92) ~[craftbukkit-1.11.2.jar:git-Bukkit-cb61ac0]
        at org.bukkit.craftbukkit.v1_11_R1.inventory.CraftInventory.contains(CraftInventory.java:102) ~[craftbukkit-1.11.2.jar:git-Bukkit-cb61ac0]
        at com.github.catageek.BookFileSystem.TestListener.onVehicleCreate(TestListener.java:18) ~[bookfilesystem-1.0.0-SNAPSHOT.jar:?]
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_112]
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_112]
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_112]
        at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_112]
        at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:296) ~[craftbukkit-1.11.2.jar:git-Bukkit-cb61ac0]