Rsa97

If a typed property does not have a default value, no implicit null default value is implied (even if the property is nullable). Instead, the property is considered to be uninitialized. Reads from uninitialized properties will generate a TypeError

$parameter1_variants = [
  'variant1', 'variant2', 'variant3', ..., 'variant300'
];
...
if (in_array($_GET['parameter1'], $parameter1_variants)) {
  ...
}