Fix a fuzzy arrow warning

Closes #78

Author: nex3

CHANGELOG.md

@@ -1,3 +1,7 @@
+## 1.0.1
+
+* Fix a fuzzy arrow type warning.
+
 ## 1.0.0
 
 * **Breaking change**: The `allowTrailingOptions` argument to `new

lib/src/arg_parser.dart

@@ -88,9 +88,18 @@ class ArgParser {
       bool negatable: true,
       void callback(bool value),
       bool hide: false}) {
-    _addOption(name, abbr, help, null, null, null, defaultsTo, callback,
+    _addOption(
+        name,
+        abbr,
+        help,
+        null,
+        null,
+        null,
+        defaultsTo,
+        callback == null ? null : (value) => callback(value as bool),
         OptionType.FLAG,
-        negatable: negatable, hide: hide);
+        negatable: negatable,
+        hide: hide);
   }
 
   /// Defines a value-taking option. Throws an [ArgumentError] if:

pubspec.yaml

@@ -1,5 +1,5 @@
 name: args
-version: 1.0.1-dev
+version: 1.0.1
 author: "Dart Team <[email protected]>"
 homepage: https://github.com/dart-lang/args
 description: >