input: Write a function to count the occurrence of each character in the given string. If the string is empty, return an empty dictionary.
  assert char_occurrence("Hello, World!")=={'H': 1, 'e': 1, 'l': 3, 'o': 2, ',': 1, ' ': 1, 'W': 1, 'r': 1, 'd': 1, '!': 1}
  assert char_occurrence("Python")=={'P': 1, 'y': 1, 't': 1, 'h': 1, 'o': 1, 'n': 1}
  assert char_occurrence("")=={}
  assert char_occurrence("AaBbCc")=={'A': 1, 'a': 1, 'B': 1, 'b': 1, 'C': 1, 'c': 1}
output: def char_occurrence(s):
      if not s:
          return {}
      count = {}
      for char in s:
          if char in count:
              count[char] += 1
          else:
              count[char] = 1
      return count