Correct the default resource location of potion registry (#4117)

src/main/java/net/minecraftforge/registries/GameData.java

@@ -126,7 +126,7 @@ public class GameData
         makeRegistry(POTIONS,      Potion.class,      MAX_POTION_ID).create();
         makeRegistry(BIOMES,       Biome.class,       MAX_BIOME_ID).create();
         makeRegistry(SOUNDEVENTS,  SoundEvent.class,  MAX_SOUND_ID).create();
-        makeRegistry(POTIONTYPES,  PotionType.class,  MAX_POTIONTYPE_ID, new ResourceLocation("water")).create();
+        makeRegistry(POTIONTYPES,  PotionType.class,  MAX_POTIONTYPE_ID, new ResourceLocation("empty")).create();
         makeRegistry(ENCHANTMENTS, Enchantment.class, MAX_ENCHANTMENT_ID).create();
         makeRegistry(RECIPES,      IRecipe.class,     MAX_RECIPE_ID).disableSaving().allowModification().create();
         makeRegistry(PROFESSIONS,  VillagerProfession.class, MAX_PROFESSION_ID).create();