diff --git a/azure/functions/decorators/blob.py b/azure/functions/decorators/blob.py
index eaad9220..e3de6f7c 100644
--- a/azure/functions/decorators/blob.py
+++ b/azure/functions/decorators/blob.py
@@ -17,8 +17,8 @@ def __init__(self,
                  **kwargs):
         self.path = path
         self.connection = connection
-        if type(source) is BlobSource:
-            self.source = source.value if source else None
+        if isinstance(source, BlobSource):
+            self.source = source.value
         else:
             self.source = source
         super().__init__(name=name, data_type=data_type)