Added canRegister override to ServicePlaceholderExpansion

Ensures the provider is not null before registration, improving safety and preventing potential issues during placeholder expansion registration.

Author: NonSwag

plugin/src/main/java/net/thenextlvl/service/placeholder/ServicePlaceholderExpansion.java

@@ -34,6 +34,11 @@ protected ServicePlaceholderExpansion(ServicePlugin plugin, Class<T> providerCla
         this(plugin, "serviceio", providerClass);
     }
 
+    @Override
+    public boolean canRegister() {
+        return provider != null && super.canRegister();
+    }
+
     @Override
     public final String getIdentifier() {
         return identifier;