input: Write a python function to safely handle user input and greet the user.
  assert greet_user('John') == 'Hello, John'
  assert greet_user('Alice') == 'Hello, Alice'
  assert greet_user('') == 'There was an error parsing your name.'
output: def greet_user(name):
      if not isinstance(name, str) or not name.strip():
          return 'There was an error parsing your name.'
      return f'Hello, {name}'