[12.x] Fix Arr::dot() to convert empty arrays to null

[imhayatunnabi]

Summary

• Fixes Arr::dot() to properly flatten empty arrays by converting them to null
• Updates existing tests to reflect the new behavior
• Resolves issue where flattened arrays still contained nested empty arrays

Problem

The Arr::dot() method is documented to "flatten a multi-dimensional associative array with dots," but it was not handling empty arrays correctly. When an empty array was encountered, it was left as-is in the output, resulting in a partially flattened array that still contained nested structures.

Example of the problem:

$data = [
    'name' => 'John',
    'tags' => [],
    'address' => [
        'street' => 'Main St',
        'metadata' => [],
    ],
];

$result = Arr::dot($data);

// Before fix:
// [
//     'name' => 'John',
//     'tags' => [],                    // ❌ Still an array!
//     'address.street' => 'Main St',
//     'address.metadata' => [],        // ❌ Still an array!
// ]

// After fix:
// [
//     'name' => 'John',
//     'tags' => null,                  // ✅ Properly flattened
//     'address.street' => 'Main St',
//     'address.metadata' => null,      // ✅ Properly flattened
// ]

This caused issues when using the result with functions like array_diff() that require single-dimensional arrays.

Solution

Modified the dot() method in Arr.php to check if a value is an empty array and convert it to null instead of storing it directly. This ensures complete flattening.

Changes made:

src/Illuminate/Collections/Arr.php:179

// Before
$results[$newKey] = $value;

// After
$results[$newKey] = is_array($value) ? null : $value;

[ropi-bc]

your solution is nicer than mine, but at the same time Taylor closed my PR immediately, so probably this one will be rejected too. not a patch-version level fix.

[ropi-bc]

->expectsOutput(' empty_array ........................................... null ') would look nicer

[imhayatunnabi]

But this was for the best test resiliency also had issue with php 8.3 testing. You can have look on the first commit

[taylorotwell]

Thanks for your pull request to Laravel!

Unfortunately, I'm going to delay merging this code for now. To preserve our ability to adequately maintain the framework, we need to be very careful regarding the amount of code we include.

If applicable, please consider releasing your code as a package so that the community can still take advantage of your contributions!