Merge pull request #7 from prokopsimek/master

feat: upgrade to be compatible with Dart 3

Author: ViolanteCodes

README.md

@@ -10,48 +10,58 @@ For a comprehensive list of examples, check out the [API documentation](https://
 
 Every resource is accessed via your butter instance:
 
-    Butter butter = Butter('YOUR_API_KEY');
+```dart
+Butter butter = Butter('YOUR_API_KEY');
 
-   OR 
+OR 
 
-    var butter = Butter('YOUR_API_KEY');
+var butter = Butter('YOUR_API_KEY');
+```
 
 Every resource method returns a Future:
 
-    // Get blog posts
-    butter.post.list({'page': '1', 'pageSize': '10'}).then((response) {
-      print(response);
-    });
+```dart
+// Get blog posts
+butter.post.list({'page': '1', 'pageSize': '10'}).then((response) {
+  print(response);
+});
+```
 
 ## Pages
 
    * page
       *     retrieve(page_type, page_slug[, params])
       *     list(page_type[, params])
-      
-    // Get page
-    butter.page.retrieve('casestudy', 'acme-co').then((response) {
-      print(response);
-    });
+
+```dart
+// Get page
+butter.page.retrieve('casestudy', 'acme-co').then((response) {
+  print(response);
+});
+```
 
 ## Content fields
 
    * content
       *     retrieve(keys)
 
-    // Get FAQ
-    butter.content.retrieve(["demo-key"]).then((resp) {
-      print(resp);
-    });
+```dart
+// Get FAQ
+butter.content.retrieve(["demo-key"]).then((resp) {
+  print(resp);
+});
+```
 
 ### Localization
 
 Setup locales in the ButterCMS dashboard and fetch localized content using the locale option:
 
-    // Get FAQ
-    butter.content.retrieve(["faq"], {'locale': 'es'}).then((resp) {
-      print(resp);
-    });
+```dart
+// Get FAQ
+butter.content.retrieve(["faq"], {'locale': 'es'}).then((resp) {
+  print(resp);
+});
+```
 
 ## Blog Engine
 

lib/src/butter.dart

@@ -9,12 +9,12 @@ class Butter {
   /// The API token for Butter user
   final String _apiKey;
 
-  Pages? page;
-  Content? content;
-  Posts? post;
-  Authors? author;
-  Categories? category;
-  Tags? tag;
+  late Pages page;
+  late Content content;
+  late Posts post;
+  late Authors author;
+  late Categories category;
+  late Tags tag;
 
   Butter(this._apiKey) {
     if (_apiKey == "") {