fallback to default locate logic if no API found

patches/server/Add-StructuresLocateEvent.patch

@@ -85,17 +85,19 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +        final var paperRegistry = io.papermc.paper.registry.PaperRegistry.getRegistry(io.papermc.paper.registry.RegistryKey.CONFIGURED_STRUCTURE_REGISTRY);
 +        final List<io.papermc.paper.world.structure.ConfiguredStructure> configuredStructures = new ArrayList<>();
 +        paperRegistry.convertToApi(structures, configuredStructures::add, false); // gracefully handle missing api, use tests to check (or exclude)
-+        final io.papermc.paper.event.world.StructuresLocateEvent event = new io.papermc.paper.event.world.StructuresLocateEvent(bukkitWorld, origin, configuredStructures, radius, skipReferencedStructures);
-+        if (!event.callEvent()) {
-+            return null;
++        if (!configuredStructures.isEmpty()) {
++            final io.papermc.paper.event.world.StructuresLocateEvent event = new io.papermc.paper.event.world.StructuresLocateEvent(bukkitWorld, origin, configuredStructures, radius, skipReferencedStructures);
++            if (!event.callEvent()) {
++                return null;
++            }
++            if (event.getResult() != null) {
++                return Pair.of(net.minecraft.server.MCUtil.toBlockPosition(event.getResult().position()), paperRegistry.getMinecraftHolder(event.getResult().configuredStructure()));
++            }
++            center = net.minecraft.server.MCUtil.toBlockPosition(event.getOrigin());
++            radius = event.getRadius();
++            skipReferencedStructures = event.shouldFindUnexplored();
++            structures = HolderSet.direct(paperRegistry::getMinecraftHolder, event.getConfiguredStructures());
 +        }
-+        if (event.getResult() != null) {
-+            return Pair.of(net.minecraft.server.MCUtil.toBlockPosition(event.getResult().position()), paperRegistry.getMinecraftHolder(event.getResult().configuredStructure()));
-+        }
-+        center = net.minecraft.server.MCUtil.toBlockPosition(event.getOrigin());
-+        radius = event.getRadius();
-+        skipReferencedStructures = event.shouldFindUnexplored();
-+        structures = HolderSet.direct(paperRegistry::getMinecraftHolder, event.getConfiguredStructures());
 +        // Paper end
          Map<StructurePlacement, Set<Holder<Structure>>> map = new Object2ObjectArrayMap();
          Iterator iterator = structures.iterator();