diff --git a/cli/fileformat.py b/cli/fileformat.py
index 1708de4..3b89c90 100644
--- a/cli/fileformat.py
+++ b/cli/fileformat.py
@@ -55,6 +55,8 @@ class CommitFormatSyntaxError(Exception):
     pass
 
 def read_field_value_str(val):
+    if val.strip() == '':
+        return None
     return '\n'.join(map(lambda x: x.strip(), val.split('\n'))).strip()
 
 def read_field_value_int(val):