fix all of the javadoc warnings

api/src/main/java/lol/pyr/znpcsplus/api/NpcApiProvider.java

@@ -30,6 +30,9 @@ public class NpcApiProvider {
     /**
      * Internal method used to register the main instance of the plugin as the api provider
      * You probably shouldn't call this method under any circumstances
+     *
+     * @param plugin Instance of the ZNPCsPlus plugin
+     * @param api Instance of the ZNPCsPlus api
      */
     public static void register(Plugin plugin, NpcApi api) {
         NpcApiProvider.api = api;

api/src/main/java/lol/pyr/znpcsplus/api/npc/NpcRegistry.java

@@ -41,7 +41,7 @@ public interface NpcRegistry {
      * @param world The {@link World} of the NPC entry
      * @param type The {@link NpcType} of the NPC entry
      * @param location The {@link NpcLocation} of the NPC entry
-     * @return
+     * @return The entry of the newly created npc
      */
     NpcEntry create(String id, World world, NpcType type, NpcLocation location);
 

api/src/main/java/lol/pyr/znpcsplus/api/npc/NpcTypeRegistry.java

@@ -9,11 +9,13 @@ public interface NpcTypeRegistry {
     /**
      * Gets a NPC type by name.
      * @param name The name of the NPC type.
+     * @return The type that is represented by the name or null if it doesnt exist
      */
     NpcType getByName(String name);
 
     /**
      * Gets all NPC types.
+     * @return all of the npc types
      */
     Collection<NpcType> getAll();
 }