diff --git a/lib/src/bindings/commit.dart b/lib/src/bindings/commit.dart
index 0e320fe..c43344b 100644
--- a/lib/src/bindings/commit.dart
+++ b/lib/src/bindings/commit.dart
@@ -73,21 +73,19 @@ void annotatedFree(Pointer<git_annotated_commit> commit) {
 /// Throws a [LibGit2Error] if error occured.
 Pointer<git_oid> create(
   Pointer<git_repository> repo,
-  String updateRef,
+  String? updateRef,
   Pointer<git_signature> author,
   Pointer<git_signature> committer,
-  String messageEncoding,
+  String? messageEncoding,
   String message,
   Pointer<git_tree> tree,
   int parentCount,
   List<String> parents,
 ) {
   final out = calloc<git_oid>();
-  final updateRefC =
-      updateRef.isEmpty ? nullptr : updateRef.toNativeUtf8().cast<Int8>();
-  final messageEncodingC = messageEncoding.isEmpty
-      ? nullptr
-      : messageEncoding.toNativeUtf8().cast<Int8>();
+  final updateRefC = updateRef?.toNativeUtf8().cast<Int8>() ?? nullptr;
+  final messageEncodingC =
+      messageEncoding?.toNativeUtf8().cast<Int8>() ?? nullptr;
   final messageC = message.toNativeUtf8().cast<Int8>();
   Pointer<Pointer<git_commit>> parentsC =
       calloc.call<Pointer<git_commit>>(parentCount);
diff --git a/lib/src/bindings/remote.dart b/lib/src/bindings/remote.dart
index 49ce350..aeb1623 100644
--- a/lib/src/bindings/remote.dart
+++ b/lib/src/bindings/remote.dart
@@ -296,7 +296,7 @@ void addPush(Pointer<git_repository> repo, String remote, String refspec) {
 void connect(
   Pointer<git_remote> remote,
   int direction,
-  String proxyOption,
+  String? proxyOption,
 ) {
   final callbacks = calloc<git_remote_callbacks>();
   final callbacksError = libgit2.git_remote_init_callbacks(
@@ -380,9 +380,9 @@ List<Map<String, dynamic>> lsRemotes(Pointer<git_remote> remote) {
 void fetch(
   Pointer<git_remote> remote,
   List<String> refspecs,
-  String reflogMessage,
+  String? reflogMessage,
   int prune,
-  String proxyOption,
+  String? proxyOption,
 ) {
   var refspecsC = calloc<git_strarray>();
   final refspecsPointers =
@@ -411,9 +411,7 @@ void fetch(
   opts.ref.prune = prune;
   opts.ref.proxy_opts = proxyOptions.ref;
 
-  final reflogMessageC = reflogMessage.isEmpty
-      ? nullptr
-      : reflogMessage.toNativeUtf8().cast<Int8>();
+  final reflogMessageC = reflogMessage?.toNativeUtf8().cast<Int8>() ?? nullptr;
 
   final error = libgit2.git_remote_fetch(
     remote,
@@ -428,6 +426,7 @@ void fetch(
   calloc.free(strArray);
   calloc.free(refspecsC);
   calloc.free(proxyOptions);
+  calloc.free(reflogMessageC);
   calloc.free(opts);
 
   if (error < 0) {
@@ -441,7 +440,7 @@ void fetch(
 void push(
   Pointer<git_remote> remote,
   List<String> refspecs,
-  String proxyOption,
+  String? proxyOption,
 ) {
   var refspecsC = calloc<git_strarray>();
   final refspecsPointers =
@@ -527,7 +526,7 @@ void prune(Pointer<git_remote> remote) {
 void free(Pointer<git_remote> remote) => libgit2.git_remote_free(remote);
 
 /// Initializes git_proxy_options structure.
-Pointer<git_proxy_options> _proxyOptionsInit(String proxyOption) {
+Pointer<git_proxy_options> _proxyOptionsInit(String? proxyOption) {
   final proxyOptions = calloc<git_proxy_options>();
   final proxyOptionsError =
       libgit2.git_proxy_options_init(proxyOptions, GIT_PROXY_OPTIONS_VERSION);
@@ -536,7 +535,7 @@ Pointer<git_proxy_options> _proxyOptionsInit(String proxyOption) {
     throw LibGit2Error(libgit2.git_error_last());
   }
 
-  if (proxyOption.isEmpty) {
+  if (proxyOption == null) {
     proxyOptions.ref.type = git_proxy_t.GIT_PROXY_NONE;
   } else if (proxyOption == 'auto') {
     proxyOptions.ref.type = git_proxy_t.GIT_PROXY_AUTO;
diff --git a/lib/src/bindings/repository.dart b/lib/src/bindings/repository.dart
index 23cf210..72caf75 100644
--- a/lib/src/bindings/repository.dart
+++ b/lib/src/bindings/repository.dart
@@ -51,12 +51,17 @@ Pointer<git_repository> openBare(String barePath) {
 /// The method will automatically detect if the repository is bare (if there is a repository).
 ///
 /// Throws a [LibGit2Error] if error occured.
-String discover(String startPath, String ceilingDirs) {
+String discover(String startPath, String? ceilingDirs) {
   final out = calloc<git_buf>(sizeOf<git_buf>());
   final startPathC = startPath.toNativeUtf8().cast<Int8>();
-  final ceilingDirsC = ceilingDirs.toNativeUtf8().cast<Int8>();
-  final error =
-      libgit2.git_repository_discover(out, startPathC, 0, ceilingDirsC);
+  final ceilingDirsC = ceilingDirs?.toNativeUtf8().cast<Int8>() ?? nullptr;
+
+  final error = libgit2.git_repository_discover(
+    out,
+    startPathC,
+    0,
+    ceilingDirsC,
+  );
 
   calloc.free(startPathC);
   calloc.free(ceilingDirsC);
@@ -77,24 +82,19 @@ Pointer<git_repository> init(
   String path,
   int flags,
   int mode,
-  String workdirPath,
-  String description,
-  String templatePath,
-  String initialHead,
-  String originUrl,
+  String? workdirPath,
+  String? description,
+  String? templatePath,
+  String? initialHead,
+  String? originUrl,
 ) {
   final out = calloc<Pointer<git_repository>>();
   final pathC = path.toNativeUtf8().cast<Int8>();
-  final workdirPathC =
-      workdirPath.isEmpty ? nullptr : workdirPath.toNativeUtf8().cast<Int8>();
-  final descriptionC =
-      description.isEmpty ? nullptr : description.toNativeUtf8().cast<Int8>();
-  final templatePathC =
-      templatePath.isEmpty ? nullptr : templatePath.toNativeUtf8().cast<Int8>();
-  final initialHeadC =
-      initialHead.isEmpty ? nullptr : initialHead.toNativeUtf8().cast<Int8>();
-  final originUrlC =
-      originUrl.isEmpty ? nullptr : originUrl.toNativeUtf8().cast<Int8>();
+  final workdirPathC = workdirPath?.toNativeUtf8().cast<Int8>() ?? nullptr;
+  final descriptionC = description?.toNativeUtf8().cast<Int8>() ?? nullptr;
+  final templatePathC = templatePath?.toNativeUtf8().cast<Int8>() ?? nullptr;
+  final initialHeadC = initialHead?.toNativeUtf8().cast<Int8>() ?? nullptr;
+  final originUrlC = originUrl?.toNativeUtf8().cast<Int8>() ?? nullptr;
   final opts = calloc<git_repository_init_options>();
   final optsError = libgit2.git_repository_init_options_init(
     opts,
@@ -139,14 +139,13 @@ Pointer<git_repository> clone(
   bool bare,
   Remote Function(Repository, String, String)? remote,
   Repository Function(String, bool)? repository,
-  String checkoutBranch,
+  String? checkoutBranch,
 ) {
   final out = calloc<Pointer<git_repository>>();
   final urlC = url.toNativeUtf8().cast<Int8>();
   final localPathC = localPath.toNativeUtf8().cast<Int8>();
-  final checkoutBranchC = checkoutBranch.isEmpty
-      ? nullptr
-      : checkoutBranch.toNativeUtf8().cast<Int8>();
+  final checkoutBranchC =
+      checkoutBranch?.toNativeUtf8().cast<Int8>() ?? nullptr;
 
   final cloneOptions = calloc<git_clone_options>();
   final cloneOptionsError =
diff --git a/lib/src/bindings/stash.dart b/lib/src/bindings/stash.dart
index e98b534..fb9f782 100644
--- a/lib/src/bindings/stash.dart
+++ b/lib/src/bindings/stash.dart
@@ -13,12 +13,11 @@ import '../util.dart';
 Pointer<git_oid> stash(
   Pointer<git_repository> repo,
   Pointer<git_signature> stasher,
-  String message,
+  String? message,
   int flags,
 ) {
   final out = calloc<git_oid>();
-  final messageC =
-      message.isNotEmpty ? message.toNativeUtf8().cast<Int8>() : nullptr;
+  final messageC = message?.toNativeUtf8().cast<Int8>() ?? nullptr;
   final error = libgit2.git_stash_save(out, repo, stasher, messageC, flags);
 
   if (error < 0) {
diff --git a/lib/src/commit.dart b/lib/src/commit.dart
index 5a00997..d2e4cdc 100644
--- a/lib/src/commit.dart
+++ b/lib/src/commit.dart
@@ -47,8 +47,8 @@ class Commit {
     required Signature commiter,
     required String treeSHA,
     required List<String> parents,
-    String updateRef = '',
-    String messageEncoding = '',
+    String? updateRef,
+    String? messageEncoding,
   }) {
     final tree = Tree.lookup(repo, treeSHA);
 
diff --git a/lib/src/remote.dart b/lib/src/remote.dart
index 080e1a2..ae3196a 100644
--- a/lib/src/remote.dart
+++ b/lib/src/remote.dart
@@ -43,9 +43,9 @@ class Remotes {
   Remote create({
     required String name,
     required String url,
-    String fetch = '',
+    String? fetch,
   }) {
-    if (fetch.isEmpty) {
+    if (fetch == null) {
       return Remote(bindings.create(_repoPointer, name, url));
     } else {
       return Remote(bindings.createWithFetchSpec(
@@ -154,7 +154,7 @@ class Remote {
   /// specified url. By default connection isn't done through proxy.
   ///
   /// Throws a [LibGit2Error] if error occured.
-  List<Map<String, dynamic>> ls([String proxy = '']) {
+  List<Map<String, dynamic>> ls([String? proxy]) {
     bindings.connect(_remotePointer, GitDirection.fetch.value, proxy);
     final result = bindings.lsRemotes(_remotePointer);
     bindings.disconnect(_remotePointer);
@@ -171,9 +171,9 @@ class Remote {
   /// Throws a [LibGit2Error] if error occured.
   TransferProgress fetch({
     List<String> refspecs = const [],
-    String reflogMessage = '',
+    String? reflogMessage,
     GitFetchPrune prune = GitFetchPrune.unspecified,
-    String proxy = '',
+    String? proxy,
   }) {
     bindings.fetch(_remotePointer, refspecs, reflogMessage, prune.value, proxy);
     return TransferProgress(bindings.stats(_remotePointer));
@@ -182,7 +182,7 @@ class Remote {
   /// Performs a push.
   ///
   /// Throws a [LibGit2Error] if error occured.
-  void push(List<String> refspecs, [String proxy = '']) {
+  void push(List<String> refspecs, [String? proxy]) {
     bindings.push(_remotePointer, refspecs, proxy);
   }
 
diff --git a/lib/src/repository.dart b/lib/src/repository.dart
index d444aa6..fa61fcb 100644
--- a/lib/src/repository.dart
+++ b/lib/src/repository.dart
@@ -45,11 +45,11 @@ class Repository {
     bool bare = false,
     Set<GitRepositoryInit> flags = const {GitRepositoryInit.mkpath},
     int mode = 0,
-    String workdirPath = '',
-    String description = '',
-    String templatePath = '',
-    String initialHead = '',
-    String originUrl = '',
+    String? workdirPath,
+    String? description,
+    String? templatePath,
+    String? initialHead,
+    String? originUrl,
   }) {
     libgit2.git_libgit2_init();
 
@@ -106,7 +106,7 @@ class Repository {
     bool bare = false,
     Remote Function(Repository, String, String)? remote,
     Repository Function(String, bool)? repository,
-    String checkoutBranch = '',
+    String? checkoutBranch,
   }) {
     libgit2.git_libgit2_init();
 
@@ -132,7 +132,7 @@ class Repository {
   /// The method will automatically detect if the repository is bare (if there is a repository).
   ///
   /// Throws a [LibGit2Error] if error occured.
-  static String discover(String startPath, [String ceilingDirs = '']) {
+  static String discover(String startPath, [String? ceilingDirs]) {
     return bindings.discover(startPath, ceilingDirs);
   }
 
@@ -412,8 +412,8 @@ class Repository {
     required Signature commiter,
     required String treeSHA,
     required List<String> parents,
-    String updateRef = '',
-    String messageEncoding = '',
+    String? updateRef,
+    String? messageEncoding,
   }) {
     return Commit.create(
       repo: this,
@@ -737,7 +737,7 @@ class Repository {
   /// [paths] is list of files to checkout from provided reference [refName]. If paths are provided
   /// HEAD will not be set to the reference [refName].
   void checkout({
-    String refName = '',
+    String? refName,
     Set<GitCheckout> strategy = const {
       GitCheckout.safe,
       GitCheckout.recreateMissing
@@ -748,7 +748,7 @@ class Repository {
     final int strat =
         strategy.fold(0, (previousValue, e) => previousValue | e.value);
 
-    if (refName.isEmpty) {
+    if (refName == null) {
       checkout_bindings.index(_repoPointer, strat, directory, paths);
     } else if (refName == 'HEAD') {
       checkout_bindings.head(_repoPointer, strat, directory, paths);
@@ -883,7 +883,7 @@ class Repository {
   /// Throws a [LibGit2Error] if error occured.
   Oid stash({
     required Signature stasher,
-    String message = '',
+    String? message,
     bool keepIndex = false,
     bool includeUntracked = false,
     bool includeIgnored = false,