[polymer] switch comment style

tools/line_doc_comments.dart

 #!/usr/bin/env dart
 
 /// Converts block-style Doc comments in Dart code to line style.
 library line_doc_comments;
 import 'dart:io';
 
 import '../pkg/path/lib/path.dart' as path;
 
 final oneLineBlock = new RegExp(r'^(\s*)/\*\*\s?(.*)\*/\s*$');
 final startBlock = new RegExp(r'^(\s*)/\*\*(.*)$');
@@ skipping 39 matching lines @@
     var oldLine = line;
     if (inBlock) {
       // See if it's the end of the comment.
       if (endBlock.hasMatch(line)) {
         inBlock = false;
 
         // Just a pointless line, delete it!
         line = null;
       } else {
         var match = blockLine.firstMatch(line);
-        var comment = match[1];
-        if (comment != '') {
-          line = '$indent/// $comment';
-        } else {
-          line = '$indent///';
+        if (match != null) {
+          var comment = match[1];
+          if (comment != '') {
+            line = '$indent/// $comment';
+          } else {
+            line = '$indent///';
+          }
         }
       }
     } else {
       // See if it's a one-line block comment like: /** Blah. */
       var match = oneLineBlock.firstMatch(line);
       if (match != null) {
         var comment = match[2];
         if (comment != '') {
           // Remove the extra space before the `*/`
           if (comment.endsWith(' ')) {
@@ skipping 32 matching lines @@
         print('$_PURPLE$path$_NO_COLOR:$_RED$linesOut$_NO_COLOR: '
             'line exceeds 80 cols:\n    $line');
       }
 
       buffer.write('$line\n');
     }
   }
 
   return buffer.toString();
 }