use basic auth when username or password are present

Author: HugoMario

src/main/resources/handlebars/python/configuration.mustache

@@ -215,9 +215,12 @@ class Configuration(six.with_metaclass(TypeWithDefault, object)):
 
         :return: The token for basic HTTP authentication.
         """
-        return urllib3.util.make_headers(
-            basic_auth=self.username + ':' + self.password
-        ).get('authorization')
+        token = ""
+        if self.username or self.password:
+            token = urllib3.util.make_headers(
+                basic_auth=self.username + ':' + self.password
+            ).get('authorization')
+        return token
 
     def auth_settings(self):
         """Gets Auth Settings dict for api client.