将字符串初始化为 null 与空字符串

How would it matter if my C++ code (as shown below) has a string initialized as an empty string :

std::string myStr = "";
....some code to optionally populate 'myStr'...
if (myStr != "") {
    // do something
}

对比无/空初始化:

std::string myStr;
....some code to optionally populate 'myStr'...
if (myStr != NULL) {
    // do something
}

在这方面是否有任何最佳实践或陷阱?

std::string a;
if(a.empty())
{
    //do stuff. You will enter this block if the string is declared like this
}

std::string a;
if(!a.empty())
{
    //You will not enter this block now
}
a = "42";
if(!a.empty())
{
    //And now you will enter this block.
}