Fix StringScanner#[] to return nil for missing match.

adambeynon · adambeynon · commit aaf522141bc4 · 2014-04-30T14:50:44.000+01:00
This was causing a bug running our stringscanner implmentation in
javascript as `undefined` was slipping into the lexer/parser from this
method.
diff --git a/stdlib/strscan.rb b/stdlib/strscan.rb
@@ -55,6 +55,10 @@ def [](idx)
         return nil;
       }
 
+      if (match[idx] == null) {
+        return nil;
+      }
+
       return match[idx];
     }
   end
