Undefined variable: missing in - php

Question

I'm currently trying to figure out PHP. however I keep running into some errors.
this is my PHP line of code that has two errors:
1)Undefined variable: missing
2)in_array() expects parameter 2 to be array
my best guess would be the missing variable ($missing) would be missing however I defined it just above it.
the errors are in the line: if (!in_array($email, $missing))
foreach ($_POST as $key => $value) {
if (in_array($key, $expected)) {
if (!is_array($value)) {
$value = trim($value);
}
if (empty($value) && in_array($key,$required)) {
$$key = '';
$missing[] = $key;
} else {
$$key = $value;
}
}
}
if (!in_array($email, $missing)) {
$email = filter_input(INPUT_POST, 'email', FILTER_VALIDATE_EMAIL);
if (!$email){
$errors['email'] = 'use a valid mail address';
}
}

Answer 1

1)Undefined variable: missing
Yes, you've defined it, but only in one branch of the code. You don't guarantee its existence. There's obviously a situation when your variable isn't defined at all and you need to take care of it before trying to use it somewhere.
2)in_array() expects parameter 2 to be array
As the error says, you need to make 100% sure that your second parameter is indeed an array AND is defined.