What is the significance of the error message "Deprecated: substr(): Passing null to parameter #1 ($string) of type string is deprecated" in PHP?

The error message "Deprecated: substr(): Passing null to parameter #1 ($string) of type string is deprecated" indicates that the substr() function in PHP is being passed a null value as the first parameter, which is not allowed. To solve this issue, you need to ensure that the first parameter passed to substr() is a valid string and not null. You can check if the string is null before calling substr() to avoid this error.

// Check if the string is not null before using substr()
if ($string !== null) {
    $result = substr($string, $start, $length);
    // Do something with the result
} else {
    // Handle the case where the string is null
}