Fixed NullPointerException when breaking/placing a spawner (#380)

* fix: Make Util#getEntityId parameter nullable

* Removed JetBrains Nullable

* Updated to follow contribution guidelines

---------

Co-authored-by: Intelli <6790859+Intelli@users.noreply.github.com>

src/main/java/net/coreprotect/utility/Util.java

@@ -859,6 +859,10 @@ public class Util extends Queue {
     }
 
     public static int getEntityId(EntityType type) {
+        if (type == null) {
+            return -1;
+        }
+        
         return getEntityId(type.name(), true);
     }