Make metadata (almost) fail-safe

This could mean life and death, see
`new Metadata(17, MetaType1_14.Float, event.meta()).value()`
vs.
`new Metadata(17, MetaType1_14.Float, event.meta().value())`

api/src/main/java/com/viaversion/viaversion/api/minecraft/metadata/Metadata.java

@@ -22,6 +22,9 @@
  */
 package com.viaversion.viaversion.api.minecraft.metadata;
 
+import com.google.common.base.Preconditions;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
 import java.util.Objects;
 
 public final class Metadata {
@@ -29,10 +32,20 @@ public final class Metadata {
     private MetaType metaType;
     private Object value;
 
-    public Metadata(int id, MetaType metaType, Object value) {
+    /**
+     * Creates a new metadata instance.
+     *
+     * @param id       metadata index
+     * @param metaType metadata type
+     * @param value    value if present
+     * @throws NullPointerException     if the given metaType is null
+     * @throws IllegalArgumentException if the value and metaType are incompatible
+     */
+    public Metadata(int id, MetaType metaType, @Nullable Object value) {
+        Preconditions.checkNotNull(metaType);
         this.id = id;
         this.metaType = metaType;
-        this.value = value;
+        this.value = checkValue(value);
     }
 
     public int id() {
@@ -47,7 +60,14 @@ public final class Metadata {
         return metaType;
     }
 
+    /**
+     * Sets the metadata type.
+     * Update the value with {@link #setValue(Object)} in case value and type are no longer compatible.
+     *
+     * @param metaType metadata type
+     */
     public void setMetaType(MetaType metaType) {
+        Preconditions.checkNotNull(metaType);
         this.metaType = metaType;
     }
 
@@ -55,12 +75,26 @@ public final class Metadata {
         return (T) value;
     }
 
-    public Object getValue() {
+    public @Nullable Object getValue() {
         return value;
     }
 
-    public void setValue(Object value) {
+    /**
-        this.value = value;
+     * Sets the metadata value.
+     * Always call {@link #setMetaType(MetaType)} first if the output type changes.
+     *
+     * @param value value
+     * @throws IllegalArgumentException if the value and metaType are incompatible
+     */
+    public void setValue(@Nullable Object value) {
+        this.value = checkValue(value);
+    }
+
+    private Object checkValue(Object value) {
+        if (value != null && !metaType.type().getOutputClass().isAssignableFrom(value.getClass())) {
+            throw new IllegalArgumentException("Metadata value and metaType are incompatible. Type=" + metaType + ", value=" + value);
+        }
+        return value;
     }
 
     @Override

api/src/main/java/com/viaversion/viaversion/api/protocol/AbstractProtocol.java

@@ -46,7 +46,7 @@ public abstract class AbstractProtocol<C1 extends ClientboundPacketType, C2 exte
         implements Protocol<C1, C2, S1, S2> {
     private final Map<Packet, ProtocolPacket> serverbound = new HashMap<>();
     private final Map<Packet, ProtocolPacket> clientbound = new HashMap<>();
-    private final Map<Class, Object> storedObjects = new HashMap<>(); // currently only used for MetadataRewriters
+    private final Map<Class<?>, Object> storedObjects = new HashMap<>(); // currently only used for MetadataRewriters
     protected final Class<C1> oldClientboundPacketEnum;
     protected final Class<C2> newClientboundPacketEnum;
     protected final Class<S1> oldServerboundPacketEnum;

common/src/main/java/com/viaversion/viaversion/protocols/protocol1_14to1_13_2/metadata/MetadataRewriter1_14To1_13_2.java

@@ -139,14 +139,14 @@ public class MetadataRewriter1_14To1_13_2 extends EntityRewriter<Protocol1_14To1
         } else if (type.is(Entity1_14Types.VILLAGER)) {
             if (metadata.id() == 15) {
                 // plains
-                metadata.setValue(new VillagerData(2, getNewProfessionId((int) metadata.getValue()), 0));
                 metadata.setMetaType(MetaType1_14.VillagerData);
+                metadata.setValue(new VillagerData(2, getNewProfessionId((int) metadata.getValue()), 0));
             }
         } else if (type.is(Entity1_14Types.ZOMBIE_VILLAGER)) {
             if (metadata.id() == 18) {
                 // plains
-                metadata.setValue(new VillagerData(2, getNewProfessionId((int) metadata.getValue()), 0));
                 metadata.setMetaType(MetaType1_14.VillagerData);
+                metadata.setValue(new VillagerData(2, getNewProfessionId((int) metadata.getValue()), 0));
             }
         } else if (type.isOrHasParent(Entity1_14Types.ABSTRACT_ARROW)) {
             if (metadata.id() >= 9) { // New piercing
@@ -154,9 +154,10 @@ public class MetadataRewriter1_14To1_13_2 extends EntityRewriter<Protocol1_14To1
             }
         } else if (type.is(Entity1_14Types.FIREWORK_ROCKET)) {
             if (metadata.id() == 8) {
-                if (metadata.getValue().equals(0))
-                    metadata.setValue(null); // https://bugs.mojang.com/browse/MC-111480
                 metadata.setMetaType(MetaType1_14.OptVarInt);
+                if (metadata.getValue().equals(0)) {
+                    metadata.setValue(null); // https://bugs.mojang.com/browse/MC-111480
+                }
             }
         } else if (type.isOrHasParent(Entity1_14Types.ABSTRACT_SKELETON)) {
             if (metadata.id() == 14) {