Fixed crash due to null spell slot

src/main/java/com/minelittlepony/unicopia/ability/magic/Caster.java

@@ -10,7 +10,6 @@ import com.minelittlepony.unicopia.EquinePredicates;
 import com.minelittlepony.unicopia.Owned;
 import com.minelittlepony.unicopia.entity.Physics;
 import com.minelittlepony.unicopia.entity.PonyContainer;
-import com.minelittlepony.unicopia.network.EffectSync;
 import com.minelittlepony.unicopia.particle.ParticleSource;
 import com.minelittlepony.unicopia.util.VecHelper;
 
@@ -28,7 +27,7 @@ public interface Caster<E extends LivingEntity> extends Owned<E>, Levelled, Affi
 
     Physics getPhysics();
 
-    EffectSync getSpellSlot();
+    SpellContainer getSpellSlot();
 
     default void setSpell(@Nullable Spell spell) {
         getSpellSlot().put(spell);

src/main/java/com/minelittlepony/unicopia/ability/magic/SpellContainer.java

@@ -0,0 +1,44 @@
+package com.minelittlepony.unicopia.ability.magic;
+
+import java.util.Optional;
+
+import javax.annotation.Nullable;
+
+import com.minelittlepony.unicopia.ability.magic.spell.SpellPredicate;
+
+public interface SpellContainer {
+    SpellContainer EMPTY = new SpellContainer() {
+        @Override
+        public <T extends Spell> Optional<T> get(SpellPredicate<T> type, boolean update) {
+            return Optional.empty();
+        }
+
+        @Override
+        public void put(Spell effect) {
+        }
+    };
+
+    /**
+     * Gets the active effect for this caster updating it if needed.
+     */
+    default <T extends Spell> Optional<T> get(boolean update) {
+        return get(null, update);
+    }
+
+    /**
+     * Returns true if this caster has an active effect attached to it.
+     */
+    default boolean isPresent() {
+        return get(true).isPresent();
+    }
+
+    /**
+     * Gets the active effect for this caster updating it if needed.
+     */
+    <T extends Spell> Optional<T> get(@Nullable SpellPredicate<T> type, boolean update);
+
+    /**
+     * Sets the active effect.
+     */
+    void put(@Nullable Spell effect);
+}

src/main/java/com/minelittlepony/unicopia/ability/magic/Thrown.java

@@ -28,7 +28,7 @@ public interface Thrown extends Spell, ProjectileDelegate {
      *
      * @param source   The entity we are currently attached to.
      */
-    boolean onThrownTick(Caster<?> source);
+    boolean onThrownTick(MagicProjectileEntity projectile);
 
     @Override
     default void onImpact(MagicProjectileEntity projectile, BlockPos pos, BlockState state) {

src/main/java/com/minelittlepony/unicopia/entity/Living.java

@@ -6,6 +6,7 @@ import java.util.stream.Stream;
 import javax.annotation.Nullable;
 
 import com.minelittlepony.unicopia.ability.magic.Caster;
+import com.minelittlepony.unicopia.ability.magic.SpellContainer;
 import com.minelittlepony.unicopia.ability.magic.spell.SpellPredicate;
 import com.minelittlepony.unicopia.ability.magic.spell.SpellType;
 import com.minelittlepony.unicopia.item.UItems;
@@ -59,7 +60,7 @@ public abstract class Living<T extends LivingEntity> implements Equine<T>, Caste
     }
 
     @Override
-    public EffectSync getSpellSlot() {
+    public SpellContainer getSpellSlot() {
         return effectDelegate;
     }
 

src/main/java/com/minelittlepony/unicopia/network/EffectSync.java

@@ -6,6 +6,7 @@ import javax.annotation.Nullable;
 
 import com.minelittlepony.unicopia.ability.magic.Caster;
 import com.minelittlepony.unicopia.ability.magic.Spell;
+import com.minelittlepony.unicopia.ability.magic.SpellContainer;
 import com.minelittlepony.unicopia.ability.magic.spell.SpellPredicate;
 import com.minelittlepony.unicopia.ability.magic.spell.SpellType;
 
@@ -20,7 +21,7 @@ import net.minecraft.util.Identifier;
  *
  * @param <T> The owning entity
  */
-public class EffectSync {
+public class EffectSync implements SpellContainer {
 
     private Optional<Spell> spell = Optional.empty();
 
@@ -36,16 +37,7 @@ public class EffectSync {
         this.param = param;
     }
 
-    /**
+    @Override
-     * Gets the active effect for this caster updating it if needed.
-     */
-    public <T extends Spell> Optional<T> get(boolean update) {
-        return get(null, update);
-    }
-
-    /**
-     * Gets the active effect for this caster updating it if needed.
-     */
     @SuppressWarnings("unchecked")
     public <T extends Spell> Optional<T> get(@Nullable SpellPredicate<T> type, boolean update) {
         if (update) {
@@ -59,9 +51,7 @@ public class EffectSync {
         return Optional.empty();
     }
 
-    /**
+    @Override
-     * Returns true if this caster has an active effect attached to it.
-     */
     public boolean isPresent() {
         sync(false);
         return checkReference();
@@ -90,6 +80,7 @@ public class EffectSync {
         }
     }
 
+    @Override
     public void put(@Nullable Spell effect) {
         updateReference(effect);
         owner.getEntity().getDataTracker().set(param, effect == null ? new CompoundTag() : SpellType.toNBT(effect));

src/main/java/com/minelittlepony/unicopia/projectile/MagicProjectileEntity.java

@@ -7,6 +7,7 @@ import com.minelittlepony.unicopia.ability.magic.Caster;
 import com.minelittlepony.unicopia.ability.magic.Levelled;
 import com.minelittlepony.unicopia.ability.magic.Magical;
 import com.minelittlepony.unicopia.ability.magic.Spell;
+import com.minelittlepony.unicopia.ability.magic.SpellContainer;
 import com.minelittlepony.unicopia.ability.magic.spell.SpellPredicate;
 import com.minelittlepony.unicopia.ability.magic.spell.SpellType;
 import com.minelittlepony.unicopia.entity.EntityPhysics;
@@ -116,7 +117,7 @@ public class MagicProjectileEntity extends ThrownItemEntity implements Magical,
     }
 
     @Override
-    public EffectSync getSpellSlot() {
+    public SpellContainer getSpellSlot() {
         return effectDelegate;
     }