当包含它的函数依赖于$ _POST数据时，如何禁止此foreach警告

I have the following code which functions as intended when $_POST values are set, however, if no $_POST values(IE when the page is first loaded) are set I get "Warning: Invalid argument supplied for foreach() in..." $_POST is always going to be empty until the user clicks submit. I have tried empty(), isset() and now count().

if(isset($_POST['submitbtn'])){

$errors = CheckFormErrors();

    if(count($errors) == 0){
        $data = CleanFormData();
        print_r($data);
    }
}

Here is the function being called(not yet complete, but it is working):

function CleanFormData(){
    foreach($_POST as $key => $value){
        if($key == 'description'){ continue; }
        if($key == 'file'){ continue; }
        if($key == 'role'){ continue; }

        $_POST[$key] = is_array($key) ? $_POST[$key]: strip_tags($_POST[$key]);
    }
        return $_POST;
}

I thought that I could surpress the error by putting it in a conditional statement, evidently that is incorrect. A little help?

As already stated in comments, you have to check if the superglobal $_POST is empty before calling the foreach itself (inside the function), not outside the function - this way you don't have to check for !empty($_POST) every time you are calling this function.

function CleanFormData() {
    if (!empty($_POST)) {
        foreach($_POST as $key => $value) {
            // Loops here
        }
    }
    return $_POST;
}