为什么程序会给出错误的输出？

# 错误的逻辑
def calculate_average(numbers):
    total = sum(numbers)
    average = total / len(numbers)  # 这里应该是除以数量，而不是总和
    return average

# 语法错误
def print_message()
    print("Hello, World!")

# 运行时错误
def divide(a, b):
    return a / b  # 如果b为0，会引发ZeroDivisionError

def divide(a, b):
    try:
        return a / b
    except ZeroDivisionError:
        return "Error: Division by zero is not allowed."

# 数据类型错误
def add_numbers(a, b):
    return a + b  # 如果a和b是字符串，会引发TypeError

def add_numbers(a, b):
    if isinstance(a, (int, float)) and isinstance(b, (int, float)):
        return a + b
    else:
        return "Error: Both inputs must be numbers."

// 空指针错误
String str = null;
System.out.println(str.length());

String str = null;
if (str != null) {
    System.out.println(str.length());
} else {
    System.out.println("Error: String is null.");
}