如何检查是否定义了可选参数

function foo(optionalParam = 'default') {
  if (optionalParam === 'default') {
    console.log('Optional parameter is not defined');
  } else {
    console.log('Optional parameter is defined');
  }
}

foo(); // Output: Optional parameter is not defined
foo('custom'); // Output: Optional parameter is defined

def foo(optional_param=None):
    if optional_param is None:
        print('Optional parameter is not defined')
    else:
        print('Optional parameter is defined')

foo()  # Output: Optional parameter is not defined
foo('custom')  # Output: Optional parameter is defined

public class Foo {
    public void bar(ParamObject paramObject) {
        if (paramObject.optionalParam == null) {
            System.out.println("Optional parameter is not defined");
        } else {
            System.out.println("Optional parameter is defined");
        }
    }
}

public class ParamObject {
    public String optionalParam;
}

Foo foo = new Foo();
ParamObject paramObject = new ParamObject();
foo.bar(paramObject); // Output: Optional parameter is not defined

paramObject.optionalParam = "custom";
foo.bar(paramObject); // Output: Optional parameter is defined