PHP Extension - Cannot convert optional to string

[FabioBatSilva]

We are trying to migrate an application from the PHP Protobuf implementation to the C extension.
And found some inconsistency on the optional behaviour.

With the php implementation optional string values are converted to a empty string ''.
With the C extension a PHP Fatal error is triggered.

PHP Fatal error:  Uncaught Exception: Cannot convert '' to string

This is what the setter looks like for a string optional.

public function setTrueOptionalString($var)
{
    GPBUtil::checkString($var, True);
    $this->true_optional_string = $var;

    return $this;
}

The php implementation of GPBUtil::checkString the value is passed as a reference and converted from null to string(0) ""
But the C implementation of GPBUtil::checkString is empty..
So null is never converted to string before assign the message value and triggering the fatal error when the value is converted to_string

---

What version of protobuf and what language are you using?
Version: main
Language: php
OS: Linux

What did you do?

<?php
# optional_test.php
require_once('../vendor/autoload.php');
require_once('test_util.php');

use Foo\TestMessage;

$m = new TestMessage([]);

$m->setTrueOptionalString(null);

var_dump($m->getTrueOptionalString());

# Compile the extension 
./php/tests/compile_extension.sh

# Run script
php -d display_errors=on -dextension=../ext/google/protobuf/modules/protobuf.so optional_test.php

What did you expect to see

string(0) ""

What did you see instead?

PHP Fatal error:  Uncaught Exception: Cannot convert '' to string

[esrauchg]

Thanks for the report. I'm following up internally about what the expected behavior is in this case.