diff --git a/README.md b/README.md
index cf33ebe..975f2f3 100644
--- a/README.md
+++ b/README.md
@@ -82,6 +82,10 @@ For more options see `redmine create --help`.
 $ redmine update 107873 --assignee 112
 ```
 
+```
+$ redmine update 107873 --assignee ''
+```
+
 For more options see `redmine update --help`.
 
 ### Filter issues
diff --git a/redmine/cli/main.py b/redmine/cli/main.py
old mode 100644
new mode 100755
diff --git a/redmine/journal.py b/redmine/journal.py
index d5d8ef2..d7e0f8f 100644
--- a/redmine/journal.py
+++ b/redmine/journal.py
@@ -66,6 +66,8 @@ def get_details(self):
                     prefix = "Attachment"
                 elif detail["property"] == "cf":
                     continue
+                elif detail["property"] == "attr":
+                    continue
                 else:
                     raise KeyError(e)
 
diff --git a/redmine/redmine.py b/redmine/redmine.py
index 440ab7f..7244b0d 100644
--- a/redmine/redmine.py
+++ b/redmine/redmine.py
@@ -188,7 +188,7 @@ def update_issue(self, issue_id, **kwargs):
         }
 
         for field in list(fields["issue"].keys()):
-            if not fields["issue"][field]:
+            if fields["issue"][field] == None:
                 del fields["issue"][field]
 
         resp = requests.put(