Throw error when trying to register a handler with an id that is already registered

Author: OffsetMonkey538

src/main/java/top/offsetmonkey538/meshlib/api/HttpHandlerRegistry.java

@@ -24,7 +24,7 @@ public interface HttpHandlerRegistry {
      *
      * @param id your handler or mod's id
      * @param handler the {@link HttpHandler} to be registered
-     * @throws IllegalArgumentException when the provided id is empty
+     * @throws IllegalArgumentException when the provided id is empty or a handler with this id is already registered
      * @see HttpHandler
      */
     void register(@NotNull String id, @NotNull HttpHandler handler) throws IllegalArgumentException;

src/main/java/top/offsetmonkey538/meshlib/impl/HttpHandlerRegistryImpl.java

@@ -16,6 +16,7 @@ public class HttpHandlerRegistryImpl implements HttpHandlerRegistry {
     @Override
     public void register(@NotNull String id, @NotNull HttpHandler handler) throws IllegalArgumentException {
         if (id.isEmpty()) throw new IllegalArgumentException("Id may not be empty!");
+        if (handlers.containsKey(id)) throw new IllegalArgumentException("Handler with id '" + id + "' already registered!");
 
         handlers.put(id, handler);
     }