diff --git a/lib/anybase_converter.dart b/lib/anybase_converter.dart
index ecb6bd0..002fda3 100644
--- a/lib/anybase_converter.dart
+++ b/lib/anybase_converter.dart
@@ -9,10 +9,7 @@ class AnyBaseConverter {
   AnyBaseConverter(
       {this.srcAlphabet = AnyBaseConverter.DEC,
       this.dstAlphabet = AnyBaseConverter.HEX}) {
-    if (srcAlphabet == null ||
-        dstAlphabet == null ||
-        (srcAlphabet != null && srcAlphabet.isEmpty) ||
-        (dstAlphabet != null && dstAlphabet.isEmpty)) {
+    if ((srcAlphabet.isEmpty) || (dstAlphabet.isEmpty)) {
       throw Exception('Bad alphabet');
     }
     this.srcAlphabet = srcAlphabet;
@@ -68,7 +65,7 @@ class AnyBaseConverter {
         }
       }
       length = newlen;
-      result = dstAlphabet.substring(divide, divide + 1) + result;
+      result = dstAlphabet.substring(divide, divide + 1) + result.toString();
     } while (newlen != 0);
 
     return result;
diff --git a/lib/shortuuid.dart b/lib/shortuuid.dart
index a204bc4..b524dae 100644
--- a/lib/shortuuid.dart
+++ b/lib/shortuuid.dart
@@ -10,8 +10,8 @@ class ShortUuid {
       "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ!#\$%&'()*+-./:<=>?@[]^_`{|}~";
 
   static String shortv4(
-      {Map<String, dynamic> options,
-      String uuidv4 = null,
+      {Map<String, dynamic>? options,
+      String? uuidv4,
       String toAlphabet = flickrBase58}) {
     uuidv4 = uuidv4 == null ? Uuid().v4(options: options) : uuidv4;
 
@@ -26,7 +26,7 @@ class ShortUuid {
         srcAlphabet: toAlphabet, dstAlphabet: AnyBaseConverter.HEX);
     String strUuidv4 = toHex.convert(shortUuid);
     var leftPad = '';
-    var m = List<String>();
+    var m = <String>[];
 
     for (var i = 0, len = 32 - strUuidv4.length; i < len; ++i) {
       leftPad += '0';
@@ -38,8 +38,10 @@ class ShortUuid {
     if (matches.isNotEmpty) {
       var match = matches.first;
       for (var i = 1; i <= match.groupCount; i++) {
-        var matchStr = match.group(i);
-        m.add(matchStr);
+        String? matchStr = match.group(i);
+        if (matchStr != null) {
+          m.add(matchStr);
+        }
       }
     }
     return [m[0], m[1], m[2], m[3], m[4]].join('-');
diff --git a/pubspec.lock b/pubspec.lock
index 71cabcc..e327263 100644
--- a/pubspec.lock
+++ b/pubspec.lock
@@ -7,356 +7,328 @@ packages:
       name: _fe_analyzer_shared
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "4.0.0"
+    version: "38.0.0"
   analyzer:
     dependency: transitive
     description:
       name: analyzer
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.39.10"
+    version: "3.4.1"
   args:
     dependency: transitive
     description:
       name: args
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.6.0"
+    version: "2.3.0"
   async:
     dependency: transitive
     description:
       name: async
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.4.1"
+    version: "2.9.0"
   boolean_selector:
     dependency: transitive
     description:
       name: boolean_selector
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.0.0"
+    version: "2.1.0"
   charcode:
     dependency: transitive
     description:
       name: charcode
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.1.3"
+    version: "1.3.1"
   collection:
     dependency: transitive
     description:
       name: collection
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.14.13"
+    version: "1.16.0"
   convert:
     dependency: transitive
     description:
       name: convert
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.1.1"
+    version: "3.0.1"
   coverage:
     dependency: transitive
     description:
       name: coverage
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.14.0"
+    version: "1.2.0"
   crypto:
     dependency: transitive
     description:
       name: crypto
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.1.5"
-  csslib:
-    dependency: transitive
-    description:
-      name: csslib
-      url: "https://pub.dartlang.org"
-    source: hosted
-    version: "0.16.1"
-  glob:
+    version: "3.0.1"
+  file:
     dependency: transitive
     description:
-      name: glob
+      name: file
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.2.0"
-  html:
+    version: "6.1.2"
+  frontend_server_client:
     dependency: transitive
     description:
-      name: html
+      name: frontend_server_client
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.14.0+3"
-  http:
+    version: "2.1.2"
+  glob:
     dependency: transitive
     description:
-      name: http
+      name: glob
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.12.1"
+    version: "2.0.2"
   http_multi_server:
     dependency: transitive
     description:
       name: http_multi_server
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.2.0"
+    version: "3.2.0"
   http_parser:
     dependency: transitive
     description:
       name: http_parser
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "3.1.4"
+    version: "4.0.0"
   io:
     dependency: transitive
     description:
       name: io
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.3.4"
+    version: "1.0.3"
   js:
     dependency: transitive
     description:
       name: js
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.6.2"
+    version: "0.6.4"
   logging:
     dependency: transitive
     description:
       name: logging
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.11.4"
+    version: "1.0.2"
   matcher:
     dependency: transitive
     description:
       name: matcher
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.12.8"
+    version: "0.12.11"
   meta:
     dependency: transitive
     description:
       name: meta
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.1.8"
+    version: "1.7.0"
   mime:
     dependency: transitive
     description:
       name: mime
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.9.6+3"
-  node_interop:
-    dependency: transitive
-    description:
-      name: node_interop
-      url: "https://pub.dartlang.org"
-    source: hosted
-    version: "1.1.1"
-  node_io:
-    dependency: transitive
-    description:
-      name: node_io
-      url: "https://pub.dartlang.org"
-    source: hosted
-    version: "1.1.1"
+    version: "1.0.1"
   node_preamble:
     dependency: transitive
     description:
       name: node_preamble
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.4.12"
+    version: "2.0.1"
   package_config:
     dependency: transitive
     description:
       name: package_config
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.9.3"
+    version: "2.0.2"
   path:
     dependency: transitive
     description:
       name: path
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.7.0"
-  pedantic:
-    dependency: transitive
-    description:
-      name: pedantic
-      url: "https://pub.dartlang.org"
-    source: hosted
-    version: "1.9.0"
+    version: "1.8.1"
   pool:
     dependency: transitive
     description:
       name: pool
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.4.0"
+    version: "1.5.0"
   pub_semver:
     dependency: transitive
     description:
       name: pub_semver
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.4.4"
+    version: "2.1.1"
   shelf:
     dependency: transitive
     description:
       name: shelf
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.7.7"
+    version: "1.3.0"
   shelf_packages_handler:
     dependency: transitive
     description:
       name: shelf_packages_handler
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.0.0"
+    version: "3.0.0"
   shelf_static:
     dependency: transitive
     description:
       name: shelf_static
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.2.8"
+    version: "1.1.0"
   shelf_web_socket:
     dependency: transitive
     description:
       name: shelf_web_socket
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.2.3"
+    version: "1.0.1"
   source_map_stack_trace:
     dependency: transitive
     description:
       name: source_map_stack_trace
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.0.0"
+    version: "2.1.0"
   source_maps:
     dependency: transitive
     description:
       name: source_maps
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.10.9"
+    version: "0.10.10"
   source_span:
     dependency: transitive
     description:
       name: source_span
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.7.0"
+    version: "1.8.2"
   stack_trace:
     dependency: transitive
     description:
       name: stack_trace
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.9.3"
+    version: "1.10.0"
   stream_channel:
     dependency: transitive
     description:
       name: stream_channel
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.0.0"
+    version: "2.1.0"
   string_scanner:
     dependency: transitive
     description:
       name: string_scanner
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.0.5"
+    version: "1.1.0"
   term_glyph:
     dependency: transitive
     description:
       name: term_glyph
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.1.0"
+    version: "1.2.0"
   test:
     dependency: "direct dev"
     description:
       name: test
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.15.1"
+    version: "1.20.2"
   test_api:
     dependency: transitive
     description:
       name: test_api
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.2.17"
+    version: "0.4.9"
   test_core:
     dependency: transitive
     description:
       name: test_core
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.3.9"
+    version: "0.4.11"
   typed_data:
     dependency: transitive
     description:
       name: typed_data
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.1.6"
+    version: "1.3.0"
   uuid:
     dependency: "direct main"
     description:
       name: uuid
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.1.0"
+    version: "3.0.6"
   vm_service:
     dependency: transitive
     description:
       name: vm_service
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "4.1.0"
+    version: "8.2.2"
   watcher:
     dependency: transitive
     description:
       name: watcher
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.9.7+15"
+    version: "1.0.1"
   web_socket_channel:
     dependency: transitive
     description:
       name: web_socket_channel
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.1.0"
+    version: "2.1.0"
   webkit_inspection_protocol:
     dependency: transitive
     description:
       name: webkit_inspection_protocol
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.7.3"
+    version: "1.0.0"
   yaml:
     dependency: transitive
     description:
       name: yaml
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.2.1"
+    version: "3.1.0"
 sdks:
-  dart: ">=2.7.0 <3.0.0"
+  dart: ">=2.16.0 <3.0.0"
diff --git a/pubspec.yaml b/pubspec.yaml
index 9b8bc25..36e7d62 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -6,10 +6,10 @@ homepage: https://github.com/coolmate/shortuuid
 repository: https://github.com/coolmate/shortuuid
 
 environment:
-  sdk: ">=2.7.0 <3.0.0"
+  sdk: ">=2.12.0 <3.0.0"
 
 dependencies:
-  uuid: ^2.1.0
+  uuid: ^3.0.1
 
 dev_dependencies:
   test: any
\ No newline at end of file