Apply suggestions from code review

Co-authored-by: Sebastian Stenzel <overheadhunter@users.noreply.github.com>

Author: infeo

src/main/java/org/cryptomator/cryptofs/CryptoFileSystemImpl.java

@@ -18,7 +18,7 @@
 import org.cryptomator.cryptofs.common.DeletingFileVisitor;
 import org.cryptomator.cryptofs.common.FinallyUtil;
 import org.cryptomator.cryptofs.dir.CiphertextDirectoryDeleter;
-import org.cryptomator.cryptofs.dir.ExcludeDirIdBackupFilter;
+import org.cryptomator.cryptofs.dir.DirectoryStreamFilters;
 import org.cryptomator.cryptofs.dir.DirectoryStreamFactory;
 import org.cryptomator.cryptofs.fh.OpenCryptoFiles;
 import org.cryptomator.cryptolib.api.Cryptor;
@@ -624,7 +624,7 @@ private void moveDirectory(CryptoPath cleartextSource, CryptoPath cleartextTarge
 			// check if dir is empty:
 			Path targetCiphertextDirContentDir = cryptoPathMapper.getCiphertextDir(cleartextTarget).path;
 			boolean targetCiphertextDirExists = true;
-			try (DirectoryStream<Path> ds = Files.newDirectoryStream(targetCiphertextDirContentDir, new ExcludeDirIdBackupFilter())) {
+			try (DirectoryStream<Path> ds = Files.newDirectoryStream(targetCiphertextDirContentDir, DirectoryStreamFilters.EXCLUDE_DIR_ID_BACKUP)) {
 				if (ds.iterator().hasNext()) {
 					throw new DirectoryNotEmptyException(cleartextTarget.toString());
 				}

src/main/java/org/cryptomator/cryptofs/dir/DirectoryStreamFilters.java

@@ -0,0 +1,12 @@
+package org.cryptomator.cryptofs.dir;
+
+import org.cryptomator.cryptofs.common.Constants;
+
+import java.nio.file.DirectoryStream;
+import java.nio.file.Path;
+
+public interface DirectoryStreamFilters {
+
+	static DirectoryStream.Filter<Path> EXCLUDE_DIR_ID_BACKUP = p -> !p.equals(p.resolveSibling(Constants.DIR_BACKUP_FILE_NAME));
+
+}