In PHP, if I have a function written like this

function example($argument1, $argument2="", $argument3="")

And I can call this function in other place like this

example($argument1)

But if I want to give some value to the thrid argument, Should I do this

example($argument1, "", "test");

Or

 example($argument1, NULL, "test");

I think both will work but what is the better way? Because in future if the value for the $argument2 is changed in the main function and if I have "", then will there be any problem? Or NULL is the best option?

Thanks

php arguments
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