Extract ProcessWire Page fields

functions.php

/**
 * Extract the specified fields from the passed page and returns it as a stdClass
 * object with properties based on the field names.
 * 
 * @var Page $page The page to extract fields from.
 * @var array $fields An array of field names to extract.
 * @var array $internal_fields Additional internal fields to extract.
 */
function extractPageFields(
    Page $page,
    array $fields,
    array $internal_fields = ['name', 'modified', 'id'],
    array $image_sizes = [360, 576, 768, 1200, 1536]
): object {
    $data = new class{};
    foreach ($internal_fields as $field) {
        $data->{$field} = $page->{$field};
    }
    foreach ($fields as $field) {
        $type = $page->fields->{$field}->getFieldType();
        if ($type instanceof FieldtypeImage) {
            if ($page->{$field} instanceof Pageimage) {
                // extract single images as one item
                $data->{$field} = new class {};
                $data->{$field}->description = $page->{$field}->description();
                $data->{$field}->path = dirname($page->{$field}->url()) . '/';
                if (!empty($image_sizes)) {
                    $data->{$field}->sizes = generateSizes($page->{$field}, $image_sizes);
                }
            } elseif ($page->{$field} instanceof Pageimages) {
                // extract multiple images as an array
                $data->{$field} = [];
                foreach ($page->{$field} as $image) {
                    $current = new class {};
                    $current->description = $image->description();
                    $current->path = dirname($image->url()) . '/';
                    if (!empty($image_sizes)) {
                        $current->sizes = generateSizes($image, $image_sizes);
                    }
                    $data->{$field}[] = $current;
                }
            } elseif ($page->{$field} === NULL) {
                // do nothing if the field is empty
            } else {
                throw new \Exception('Unknown field type.');
            }
        } elseif ($type instanceof FieldtypePage) {
            $data->{$field} = [];
            foreach ($page->{$field} as $item) {
                $data->{$field}[] = $item->id;
            }
        } elseif ($type instanceof FieldtypeTextareas) {
            foreach ($page->{$field} as $name => $item) {
                $data->{$name} = $item;
            }
        } elseif ($type instanceof FieldtypeRepeater) {
            $data->{$field} = [];
            foreach ($page->{$field} as $item) {
                $data->{$field}[] = extractAllPageFields($item, []);
            }
        } else {
            $data->{$field} = $page->get($field);
        }
    }
    return $data;
}



/**
 * Generate alternate image sizes for the given image. Returns an array containing
 * objects for all created sizes, with "w" as the width and "file" as the basename
 * of the file (no need to include the full path each time). Doesn't create variants
 * larger than the original image.
 *
 * @param Pageimage $image The image to create variants of.
 * @param array $sizes An array of integers (the sizes you want).
 * @return void
 */
function generateSizes(Pageimage $image, array $sizes): array {
    sort($sizes);
    $generated = [];
    foreach ($sizes as $size) {
        $current = new class {};
        if ($image->width() >= $size) {
            $current->w = $size;
            $current->file = basename($image->width($size)->url());
            $generated[] = $current;
        } else {
            // if the requested size is higher than the size of the original, 
            // include the original as is and stop the loop
            $current->w = $image->width();
            $current->file = basename($image->url());
            $generated[] = $current;
            break;
        }
    }
    return $generated;
}

This borks at line : 54
{"error":"Error: Trying to get property 'id' of non-object.