input: Write a function to count the occurrence of each character in a given string. The function should return a dictionary where the keys are the characters and the values are their respective counts. If the input string is empty, return an empty dictionary.
  
  assert char_occurrences("Hello, World!") == {'H': 1, 'e': 1, 'l': 3, 'o': 2, ',': 1, ' ': 1, 'W': 1, 'r': 1, 'd': 1, '!': 1}
  assert char_occurrences("") == {}
  assert char_occurrences("aaaa") == {'a': 4}
  assert char_occurrences("aAaA") == {'a': 2, 'A': 2}
output: def char_occurrences(s):
      if not s:
          return {}
      count_dict = {}
      for char in s:
          if char in count_dict:
              count_dict[char] += 1
          else:
              count_dict[char] = 1
      return count_dict