How to avoid undefined index errors on a function to detect undefined indexes in PHP?

one text

Okay, so I wrote a function to test if an array key has a value and return it, or else, return a value from the POST array, the problem is, since some of the are undefined, I get "Undefined Index error" while I'm sending the variables to see if they're defined or not.

So, what I want to know is, how to prevent this error from happening without checking if it is set before sending it to the function?

Here's some of the code I'm using:

function issetorpost($var, $post = '') {
    
    $return = '';
    
    if (isset($var) && !empty($var)) {
        $return = $var;
    }
    
    if (isset($post) && !empty($post)) {
        $return = $post;
    }
    
    return $return;
    
}

And it's used on input checks on form:

<input type="text" name="inp1" value="<?= issetorpost($fromdb['inp1'],$_POST['inp1']) ?>" />

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