Fixes NullPointer in Import Manager

The crash can happen if using a template file without a bundles section in it. 
This will fix it as bundles are not required.

Fixes #77

src/main/java/world/bentobox/magiccobblestonegenerator/managers/StoneGeneratorImportManager.java

@@ -202,7 +202,9 @@ private void createGenerators(YamlConfiguration config, @Nullable User user, Gam
 		reader = config.getConfigurationSection("bundles");
 		int bundleSize = 0;
 
-		for (String bundleId : reader.getKeys(false))
+		Set<String> keys = reader == null ? Collections.emptySet() : reader.getKeys(false);
+
+		for (String bundleId : keys)
 		{
 			GeneratorBundleObject generatorBundle = new GeneratorBundleObject();
 			generatorBundle.setUniqueId(prefix + bundleId.toLowerCase());