       callback = parameters
       parameters = {}
     parameters or= {}
+    callback or= noop
     @commands.push({ name, parameters, callback, retry })
 
   execute: () =>

sys             = require("sys")
events          = require("events")

# Include the units.
ResponseParser  = require("./response").ResponseParser
invoke          = require("./request").invoke

noop = () -> true

class AmazonEC2Client extends events.EventEmitter

                return
              if statusCode == 2
                try
                  outcome = command.callback(struct)
                catch _
                  @emit "error", [ _, responder.statusCode]
                  return
