Write a Python program that asks the user to input two lists containing only integers, and then returns a new list that contains all elements that appear in either of the original lists, without any duplicates. The program should be designed in a function that takes the two lists as arguments and returns the union list. The program should also handle any possible errors, such as invalid input types or empty lists. The output should be sorted in ascending order. Use meaningful variable names and appropriate comments to enhance program readability.
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