Review fixes

pre_commit_hooks/detect_aws_credentials.py

diff --git a/pre_commit_hooks/detect_aws_credentials.py b/pre_commit_hooks/detect_aws_credentials.py
index 9ef8fec..a744b6f 100644
--- a/pre_commit_hooks/detect_aws_credentials.py
+++ b/pre_commit_hooks/detect_aws_credentials.py
@@ -31,7 +31,7 @@
     for env_var in (
         'AWS_SECRET_ACCESS_KEY', 'AWS_SECURITY_TOKEN', 'AWS_SESSION_TOKEN',
     ):
-        if env_var in os.environ and os.environ[env_var]:
+        if os.environ.get(env_var):
             keys.add(os.environ[env_var])
     return keys