Use kwargs.get()

Author: Peter Amstutz

cwltool/workflow.py

@@ -670,7 +670,7 @@ def __init__(self, toolpath_object, pos, **kwargs):
 
         kwargs["requirements"] = (kwargs.get("requirements", []) +
                                   toolpath_object.get("requirements", []) +
-                                  get_overrides(kwargs["overrides"], self.id))
+                                  get_overrides(kwargs.get("overrides", []), self.id))
         kwargs["hints"] = kwargs.get("hints", []) + toolpath_object.get("hints", [])
 
         try: