we need to return a valid map to modify

Author: mbuckton

src/main/java/io/mapsmessaging/api/message/Message.java

@@ -305,7 +305,7 @@ ByteBuffer[] pack(Map<String, String> updatedMeta) throws IOException {
   }
 
   public Map<String, String> getMeta(){
-    return meta == null ? Map.of() : meta;
+    return meta == null ? new LinkedHashMap<>() : meta;
   }