Error in my repeat task

I got this error in my repeating task but I cannot find out what this NullPointerException is for...

Error:

Code:

[14:53:56] [Server thread/INFO]: [0;32;1mMedusaXYZ reloaded successfully.[m
[14:54:01] [Server thread/WARN]: [MedusaXYZ] Task #57 for MedusaXYZ v0.1 generated an exception
java.lang.NullPointerException
    at xyz.medusa.Core$1.run(Core.java:39) ~[?:?]
    at org.bukkit.craftbukkit.v1_8_R3.scheduler.CraftTask.run(CraftTask.java:71) ~[spigot.jar:git-Spigot-6d16e64-b105298]
    at org.bukkit.craftbukkit.v1_8_R3.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:350) [spigot.jar:git-Spigot-6d16e64-b105298]
    at net.minecraft.server.v1_8_R3.MinecraftServer.B(MinecraftServer.java:722) [spigot.jar:git-Spigot-6d16e64-b105298]
    at net.minecraft.server.v1_8_R3.DedicatedServer.B(DedicatedServer.java:374) [spigot.jar:git-Spigot-6d16e64-b105298]
    at net.minecraft.server.v1_8_R3.MinecraftServer.A(MinecraftServer.java:653) [spigot.jar:git-Spigot-6d16e64-b105298]
    at net.minecraft.server.v1_8_R3.MinecraftServer.run(MinecraftServer.java:556) [spigot.jar:git-Spigot-6d16e64-b105298]
    at java.lang.Thread.run(Unknown 

Code:

Code:

for(Player op : Bukkit.getOnlinePlayers()) {
                    for(ItemStack is : op.getInventory()) {
                        if(is.getType() == Material.NAME_TAG) {
                            if(is.hasItemMeta()) {
                                ItemMeta im = is.getItemMeta();
                                if(im.getDisplayName().equals("Name Tag")) {
                                    int amount = is.getAmount();
                                    op.getInventory().remove(is);
                                   
                                    ItemStack tag = new ItemStack(Material.NAME_TAG, amount);
                                    ItemMeta meta = tag.getItemMeta();
                                    meta.setDisplayName(ChatColor.AQUA + "Name Tag");
                                    tag.setItemMeta(meta);
                                   
                                    op.getInventory().addItem(tag);
                                }
                            }
                        }
                    }
                }

The error is on this line:

Code:

if(is.getType() == Material.NAME_TAG) {

 

if the player has empty slots in their inventory, "is" will be null
insert a != null check

 

Code:

for(ItemStack is : op.getInventory()) {
                        if(is.getType() != null) {
                            if(is.getType() == Material.NAME_TAG) {
                                if(is.hasItemMeta()) {
                                    ItemMeta im = is.getItemMeta();
                                    if(im.getDisplayName().equals("Name Tag")) {
                                        int amount = is.getAmount();
                                        op.getInventory().remove(is);
                                       
                                        ItemStack tag = new ItemStack(Material.NAME_TAG, amount);
                                        ItemMeta meta = tag.getItemMeta();
                                        meta.setDisplayName(ChatColor.AQUA + "Name Tag");
                                        tag.setItemMeta(meta);
                                       
                                        op.getInventory().addItem(tag);
                                    }
                                }
                            }
                            // ==============
                        }
                    }

NullPointerExecption at

Code:

if(is.getType() != null) {

 

check if the itemstack itself is null,
not is.getType() .-.