API-2197 check for client credentials key

bynder_sdk/client/bynder_client.py

@@ -31,7 +31,7 @@ def __init__(self, domain, **kwargs):
                 )
 
             # if client credentials use BackendApplicationClient from oauthlib, client suited for client credentials
-            client_credentials = BackendApplicationClient(kwargs['client_id']) if kwargs['client_credentials'] else None
+            client_credentials = BackendApplicationClient(kwargs['client_id']) if kwargs.get('client_credentials', None) else None
             self.session = BynderOAuth2Session(
                 domain,
                 kwargs['client_id'],