Check for cachedFiles existing

src/main/java/link/infra/packwiz/installer/UpdateManager.java

@@ -149,6 +149,7 @@ public class UpdateManager {
 		ui.submitProgress(new InstallProgress("Checking local files..."));
 
 		List<URI> invalidatedUris = new ArrayList<>();
+		if (manifest.cachedFiles != null) {
 			Iterator<Map.Entry<URI, ManifestFile.File>> it = manifest.cachedFiles.entrySet().iterator();
 			while (it.hasNext()) {
 				Map.Entry<URI, ManifestFile.File> entry = it.next();
@@ -160,6 +161,7 @@ public class UpdateManager {
 					}
 				}
 			}
+		}
 
 		if (manifest.packFileHash != null && packFileSource.hashIsEqual(manifest.packFileHash) && invalidatedUris.size() == 0) {
 			System.out.println("Modpack is already up to date!");