fix(key): Add to bom and fix checkstyle

Author: kermandev

bom/build.gradle.kts

@@ -17,6 +17,7 @@ dependencies {
       "extra-kotlin",
       "key",
       "nbt",
+      "properties",
       "serializer-configurate4",
       "text-logger-slf4j",
       "text-minimessage",

key/src/main/java/net/kyori/adventure/key/KeyImpl.java

@@ -42,7 +42,7 @@ final class KeyImpl implements Key {
   static final @RegExp String NAMESPACE_PATTERN = "[a-z0-9_\\-.]+";
   static final @RegExp String VALUE_PATTERN = "[a-z0-9_\\-./]+";
 
-  static final AdventureProperties.KeyInternStrategy INTERN_STRATEGY = AdventureProperties.KEY_INTERN_STRATEGY.value();
+  static final AdventureProperties.@Nullable KeyInternStrategy INTERN_STRATEGY = AdventureProperties.KEY_INTERN_STRATEGY.value();
 
   private final String namespace;
   private final String value;