unfortunately, it doesn't go away using default dict.  I need to have the keys in the dict with empty values and default dict doesn't give me that option.  default dict will set the value correctly when I do assign a value, but that's not what I need.  Later in the code, I look to the keys within ```all_reference_values``` and act on some set logic.  A new value may not have been added to the key, but I still need to know that the key is there.