Make it strong mode clean.

lib/src/arg_parser.dart

Index: lib/src/arg_parser.dart
diff --git a/lib/src/arg_parser.dart b/lib/src/arg_parser.dart
index f5ce41a35f6e28ec354557107afe4ecaae6e6db6..fa80031a58914f2a0f04fb1333d497843d7b6a3f 100644
--- a/lib/src/arg_parser.dart
+++ b/lib/src/arg_parser.dart
@@ -130,7 +130,7 @@ class ArgParser {
   /// Parses [args], a list of command-line arguments, matches them against the
   /// flags and options defined by this parser, and returns the result.
   ArgResults parse(List<String> args) =>
-      new Parser(null, this, args.toList(), null, null).parse();
+      new Parser(null, this, args.toList()).parse();
 
   /// Generates a string displaying usage information for the defined options.
   ///