MappingItemConverter skips null fields

[tpolman]

In Ddeboer\DataImport\ItemConverter\MappingItemConverter

    /**
     * Applies a mapping to an item
     *
     * @param array  $item
     * @param string $from
     * @param string $to
     *
     * @return array
     */
    protected function applyMapping(array $item, $from, $to)
    {
        // skip fields that dont exist
        if (!isset($item[$from])) {
            return $item;
        }

isset also skips fields which do exist but have a null value, this can be fixed by replacing the isset code (line 79) with:

if (!array_key_exists($from, $item)) { 

If you explicitly do not want to have null fields mapped then you could use another ItemConverter which filters empty keys. Or make it optional behaviour of MappingItemConverters.

Great bundle!

[ddeboer]

Ah, I recently fixed this issue in the workflow (0aeb02d) but apparently not here. Do you want to open a PR?