diff --git a/deepomatic/api/http_helper.py b/deepomatic/api/http_helper.py
index 558905e..6dc87a1 100644
--- a/deepomatic/api/http_helper.py
+++ b/deepomatic/api/http_helper.py
@@ -79,7 +79,9 @@ def __init__(self, app_id=None, api_key=None, verify_ssl=None,
             raise DeepomaticException("Please specify 'api_key' either by passing it to the client"
                                       " or by defining the DEEPOMATIC_API_KEY environment variable.")
 
-        if not isinstance(version, string_types):
+        if version is None or version == '':
+            version = ''
+        elif not isinstance(version, string_types):
             version = 'v%g' % version
         elif version[0] != 'v':
             version = 'v' + version