clean and refactor

lib/melon/passes/method_compiler.rb

@@ -32,7 +32,7 @@ module Melon
         w = Vm::Tree::CallSite.new()
         puts "receiver #{statement}"
         w.name = name
-        w.arguments = process(args)
+        w.arguments = process(args) || []
         w.receiver = process(receiver)
         w
       end