如果图案为空，则打印空值

pattern = ""
if pattern == "":
    print("空值")

String pattern = "";
if (pattern.equals("")) {
    System.out.println("空值");
}

#include <iostream>
#include <string>
using namespace std;

int main() {
    string pattern = "";
    if (pattern.empty()) {
        cout << "空值" << endl;
    }
    return 0;
}