How to list all files in a directory without nullpointer exception?

Hey there,
I am coding a schema plugin (like a schematic plugin) and I want to list all the files with a /list command in the schemas folder of the plugin, but everytimes I get the Nullpointer exception.

Code:

Code:

public boolean list(Player p) {
         File folder = new File(plugin.getDataFolder().getAbsolutePath()+"/schemas/");
         File[] listOfFiles = folder.listFiles();

             for (int i = 0; i < listOfFiles.length; i++) {
               if (listOfFiles[i].isFile()) {
                 p.sendMessage("§a" + listOfFiles[i].getName());
               } else if (listOfFiles[i].isDirectory()) {
                 p.sendMessage("§cIn the schemas directory was found an another directory:");
                 p.sendMessage(listOfFiles[i].getName());
                 p.sendMessage("§cIt will be ignored!");
               }
             }
         return false;
    }

Error:

Code:

[16:18:42 INFO]: Scrapnix issued server command: /schema list
[16:18:42 ERROR]: null
org.bukkit.command.CommandException: Unhandled exception executing command 'schema' in plugin SchematicsPlugin v1.0
    at org.bukkit.command.PluginCommand.execute(PluginCommand.java:46) ~[spigot-1.8.8.jar:git-Spigot-db6de12-18fbb24]
    at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:141) ~[spigot-1.8.8.jar:git-Spigot-db6de12-18fbb24]
    at org.bukkit.craftbukkit.v1_8_R3.CraftServer.dispatchCommand(CraftServer.java:641) ~[spigot-1.8.8.jar:git-Spigot-db6de12-18fbb24]
    at net.minecraft.server.v1_8_R3.PlayerConnection.handleCommand(PlayerConnection.java:1162) [spigot-1.8.8.jar:git-Spigot-db6de12-18fbb24]
    at net.minecraft.server.v1_8_R3.PlayerConnection.a(PlayerConnection.java:997) [spigot-1.8.8.jar:git-Spigot-db6de12-18fbb24]
    at net.minecraft.server.v1_8_R3.PacketPlayInChat.a(PacketPlayInChat.java:45) [spigot-1.8.8.jar:git-Spigot-db6de12-18fbb24]
    at net.minecraft.server.v1_8_R3.PacketPlayInChat.a(PacketPlayInChat.java:1) [spigot-1.8.8.jar:git-Spigot-db6de12-18fbb24]
    at net.minecraft.server.v1_8_R3.PlayerConnectionUtils$1.run(SourceFile:13) [spigot-1.8.8.jar:git-Spigot-db6de12-18fbb24]
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_65]
    at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_65]
    at net.minecraft.server.v1_8_R3.SystemUtils.a(SourceFile:44) [spigot-1.8.8.jar:git-Spigot-db6de12-18fbb24]
    at net.minecraft.server.v1_8_R3.MinecraftServer.B(MinecraftServer.java:715) [spigot-1.8.8.jar:git-Spigot-db6de12-18fbb24]
    at net.minecraft.server.v1_8_R3.DedicatedServer.B(DedicatedServer.java:374) [spigot-1.8.8.jar:git-Spigot-db6de12-18fbb24]
    at net.minecraft.server.v1_8_R3.MinecraftServer.A(MinecraftServer.java:654) [spigot-1.8.8.jar:git-Spigot-db6de12-18fbb24]
    at net.minecraft.server.v1_8_R3.MinecraftServer.run(MinecraftServer.java:557) [spigot-1.8.8.jar:git-Spigot-db6de12-18fbb24]
    at java.lang.Thread.run(Thread.java:745) [?:1.8.0_65]
Caused by: java.lang.NullPointerException
    at com.Scrap.Schematics.SchematicManager.list(SchematicManager.java:77) ~[?:?]
    at com.Scrap.Schematics.Main.onCommand(Main.java:63) ~[?:?]
    at org.bukkit.command.PluginCommand.execute(PluginCommand.java:44) ~[spigot-1.8.8.jar:git-Spigot-db6de12-18fbb24]
    ... 15 more

I hope someone can help me

 

@Scrapnix check if listOfFiles is not null before to loops
listFiles() return null if no files found

 

@Caderape2
Sorry, my mistake. I forgot to put return true into the end of the loop.

//close

 

@Scrapnix

Why are you still on 1.8? Please read this.

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