diff --git a/lib/sendgrid/client.rb b/lib/sendgrid/client.rb
index 1cce5f65..7e4d0991 100644
--- a/lib/sendgrid/client.rb
+++ b/lib/sendgrid/client.rb
@@ -14,7 +14,7 @@ class API
     #   - +version+ -> the version of the API you wish to access,
     #                  currently only "v3" is supported
     #
-    def initialize(api_key: nil, host: nil, request_headers: nil, version: nil)
+    def initialize(api_key: '', host: nil, request_headers: nil, version: nil)
       @api_key          = api_key
       @host             = host ? host : 'https://api.sendgrid.com'
       @version          = version ? version : 'v3'