SPIGOT-2540: Add nullability annotations to entire Bukkit API

By: Darkyenus <darkyenus@gmail.com>

paper-api/src/main/java/org/bukkit/block/Beacon.java

@@ -6,15 +6,19 @@ import org.bukkit.entity.LivingEntity;
 import org.bukkit.inventory.BeaconInventory;
 import org.bukkit.potion.PotionEffect;
 import org.bukkit.potion.PotionEffectType;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 /**
  * Represents a captured state of a beacon.
  */
 public interface Beacon extends Container, Nameable {
 
+    @NotNull
     @Override
     BeaconInventory getInventory();
 
+    @NotNull
     @Override
     BeaconInventory getSnapshotInventory();
 
@@ -27,6 +31,7 @@ public interface Beacon extends Container, Nameable {
      * @return the players in range
      * @throws IllegalStateException if this block state is not placed
      */
+    @NotNull
     Collection<LivingEntity> getEntitiesInRange();
 
     /**
@@ -43,6 +48,7 @@ public interface Beacon extends Container, Nameable {
      *
      * @return the primary effect or null if not set
      */
+    @Nullable
     PotionEffect getPrimaryEffect();
 
     /**
@@ -50,13 +56,14 @@ public interface Beacon extends Container, Nameable {
      *
      * @param effect new primary effect
      */
-    void setPrimaryEffect(PotionEffectType effect);
+    void setPrimaryEffect(@Nullable PotionEffectType effect);
 
     /**
      * Returns the secondary effect set on the beacon.
      *
      * @return the secondary effect or null if no secondary effect
      */
+    @Nullable
     PotionEffect getSecondaryEffect();
 
     /**
@@ -65,5 +72,5 @@ public interface Beacon extends Container, Nameable {
      *
      * @param effect desired secondary effect
      */
-    void setSecondaryEffect(PotionEffectType effect);
+    void setSecondaryEffect(@Nullable PotionEffectType effect);
 }