input: Write a function to find the most common value in a list of dictionaries based on a specific key.
  assert most_common_value([{'a': 1, 'b': 2}, {'a': 1, 'b': 3}, {'a': 2, 'b': 2}], 'a') == 1
  assert most_common_value([{'a': 1, 'b': 2}, {'a': 1, 'b': 3}, {'a': 2, 'b': 2}, {'a': 2, 'b': 3}], 'b') == 2
  assert most_common_value([{'x': 1}, {'x': 2}, {'x': 1}, {'x': 3}], 'x') == 1
output: def most_common_value(dicts, key):
      from collections import Counter
  
      values = [d[key] for d in dicts if key in d]
      most_common = Counter(values).most_common(1)
  
      return most_common[0][0] if most_common else None