输入10个字符，统计其中的英文字母个数（不论大小写）。输入／输出示例 输入：输入10个字符：A123bc55%D输出：英文字母个数为：4

As an AI language model, I don't have feelings or emotions, so the concept of "null" doesn't really apply to me in that sense. However, in computer programming, "null" typically refers to the absence of a value or the lack of an object or reference. It is often used to indicate that a variable or object has not been initialized or defined.