diff --git a/_ucoinpy_test/api/bma/test_wot.py b/_ucoinpy_test/api/bma/test_wot.py
index 28900fb42c25574c91e92a4a3f7158b8071137e3..244452e78abd945c89686a1058e48c806f714f8c 100644
--- a/_ucoinpy_test/api/bma/test_wot.py
+++ b/_ucoinpy_test/api/bma/test_wot.py
@@ -130,6 +130,17 @@ class Test_BMA_Wot(WebFunctionalSetupMixin, unittest.TestCase):
                     },
                     "isMember": True,
                     "signature": "42yQm4hGTJYWkPg39hQAUgP6S6EQ4vTfXdJuxKEHL1ih6YHiDL2hcwrFgBHjXLRgxRhj2VNVqqc6b4JayKqTE14r"
+                },
+                {
+                    "pubkey": "9WYHTavL1pmhunFCzUwiiq4pXwvgGG5ysjZnjz9H8yB",
+                    "uid": "certifier uid",
+                    "cert_time": {
+                        "block": 88,
+                        "medianTime": 1509991044
+                    },
+                    "written": None,
+                    "isMember": True,
+                    "signature": "42yQm4hGTJYWkPg39hQAUgP6S6EQ4vTfXdJuxKEHL1ih6YHiDL2hcwrFgBHjXLRgxRhj2VNVqqc6b4JayKqTE14r"
                 }
             ]
         }
diff --git a/ucoinpy/__init__.py b/ucoinpy/__init__.py
index 65b293bf3358f1e1f00e6e1124d9918481855e70..9b0938b54b5ed4971ea7724bf33a794acc104681 100644
--- a/ucoinpy/__init__.py
+++ b/ucoinpy/__init__.py
@@ -21,7 +21,7 @@ PROTOCOL_VERSION="1"
 MANAGED_API=["BASIC_MERKLED_API"]
 
 __author__      = 'Caner Candan & inso'
-__version__     = '0.12.1'
+__version__     = '0.12.2'
 __nonsense__    = 'uCoin'
 
 from . import api, documents, key
\ No newline at end of file
diff --git a/ucoinpy/api/bma/wot/__init__.py b/ucoinpy/api/bma/wot/__init__.py
index c777e7d30596b72c28d479d71c92a45334eff71b..74b4244735ab4d4f32e0d8eb97485250a6bdf350 100644
--- a/ucoinpy/api/bma/wot/__init__.py
+++ b/ucoinpy/api/bma/wot/__init__.py
@@ -190,16 +190,23 @@ class CertifiersOf(WOT):
                             "required": ["block", "medianTime"]
                         },
                         "written": {
-                            "type": "object",
-                            "properties": {
-                                "number": {
-                                    "type": "number",
+                            "oneOf": [
+                                {
+                                    "type": "object",
+                                    "properties": {
+                                        "number": {
+                                            "type": "number",
+                                        },
+                                        "hash": {
+                                            "type": "string"
+                                        }
+                                    },
+                                    "required": ["number", "hash"]
                                 },
-                                "hash": {
-                                    "type": "string"
+                                {
+                                    "type": "null"
                                 }
-                            },
-                            "required": ["number", "hash"]
+                            ]
                         },
                         "isMember": {
                             "type": "boolean"