I had a problem adding a product image programatically. Here's the code I used:

```
$product->setImage('/test.jpg')
    ->setSmallImage('/test.jpg')
    ->setThumbnail('/test.jpg')
    ->addImageToMediaGallery('/test.jpg', array('image','thumbnail','small_image'), false, false);

$product = $productRepository->save($product);

```

When run, it throws this error:

```
Uncaught exception 'Magento\Framework\Exception\LocalizedException' with message 'There is no MediaGalleryEntryConverter for given type' in vendor/magento/module-catalog/Model/Product/Attribute/Backend/Media/EntryConverterPool.php:48

```

when I save product and try to update like this [link](https://github.com/magento/magento2/issues/5249): `$product->save();`

Throws this error:

```
Fatal error:Uncaught InvalidArgumentException: Required parameter 'theme_dir' was not passed in .../vendor/magento/framework/View/Design/Fallback/Rule/Simple.php:61

```

Any ideas ?