def is_three_doubles(word):
    """check if a word have three consecutive double letters."""
    if word is None or len(word) < 6:
        return False
    consecutives = 0
    index = 0
    while index < len(word) - 1:
        if word[index+1] == word[index]:
            consecutives += 1
            if consecutives == 3:
                return True
            index += 2
        else:
            consecutives = 0
            index += 1
    return False