Make it strong mode clean.

lib/src/parser.dart

Index: lib/src/parser.dart
diff --git a/lib/src/parser.dart b/lib/src/parser.dart
index c36035ce37120514fa104746114ff5df7a5f9b29..55678542f1f5c519b58fc173decd6961a6dfabdb 100644
--- a/lib/src/parser.dart
+++ b/lib/src/parser.dart
@@ -35,7 +35,8 @@ class Parser {
   /// The accumulated parsed options.
   final Map<String, dynamic> results = <String, dynamic>{};
 
-  Parser(this.commandName, this.grammar, this.args, this.parent, rest) {
+  Parser(this.commandName, this.grammar, this.args,
+      [this.parent, List<String> rest]) {
     if (rest != null) this.rest.addAll(rest);

[nweiz, 2016/03/02 23:58:54]

This addAll thing seems weird. Maybe change to "rest = rest ?? <String>[]".

[Bob Nystrom, 2016/03/03 00:19:08]

It is a bit weird, but if I recall, it needs to copy the list that gets passed
to it anyway, so this accomplishes that too.

   }