修复Java对象的字段名不能为unicode类型的问题
diff --git a/dubbo/codec/encoder.py b/dubbo/codec/encoder.py
index 5ddfd88..48de9a1 100644
--- a/dubbo/codec/encoder.py
+++ b/dubbo/codec/encoder.py
@@ -38,7 +38,7 @@
         return self.__values[key]
 
     def __setitem__(self, key, value):
-        if not isinstance(key, str):
+        if not isinstance(key, (str, unicode)):
             raise ValueError('Object key {} should be string type.'.format(key))
         self.__values[key] = value