diff --git a/src/coscine/config.py b/src/coscine/config.py
index a220691740bcae7f589f32c3fa713441fbf6f60f..bb77ba2bb03ab2f75c204d938474ab5673d3ff8a 100644
--- a/src/coscine/config.py
+++ b/src/coscine/config.py
@@ -45,9 +45,9 @@ class Config:
 		3. System directory (e.g. User/AppData/Local/... on Windows)  
 	"""
 
-	token: str = None
-	language: str = None
-	concurrent: bool = True
+	token: str
+	language: str
+	concurrent: bool
 
 ###############################################################################
 
diff --git a/src/coscine/resource.py b/src/coscine/resource.py
index 30862f150944c5c6a16c6246bef306adfe7bb34f..584685c138e3e849d2f14492a3da1f803023cd2e 100644
--- a/src/coscine/resource.py
+++ b/src/coscine/resource.py
@@ -51,12 +51,12 @@ class S3info:
 	Provides a simple pythonic interface to resource S3 access data
 	"""
 
-	read_access_key: str = ""
-	read_secret_key: str = ""
-	write_access_key: str = ""
-	write_secret_key: str = ""
-	endpoint: str = ""
-	bucket: str = ""
+	read_access_key: str
+	read_secret_key: str
+	write_access_key: str
+	write_secret_key: str
+	endpoint: str
+	bucket: str
 	_data: dict
 
 	def __init__(self, data: dict) -> None:
diff --git a/src/coscine/utils.py b/src/coscine/utils.py
index de359e49252978104650079933b4d3c9b36de5aa..0097fc75fb3513f6e22e308353c9e58751ec3998 100644
--- a/src/coscine/utils.py
+++ b/src/coscine/utils.py
@@ -28,7 +28,7 @@ source like StackOverflow. Credit is given where it is due.
 from typing import List, Union
 
 ###############################################################################
-# Clas
+# Class
 ###############################################################################
 # Source: https://stackoverflow.com/questions/12523586/
 # 		  python-format-size-application-converting-b-to-kb-mb-gb-tb