/// <summary>Fills the list of words with translation.</summary>
/// <param name="material">Material.</param>
/// <returns>List of vocabulary words.</returns>
private async Task <List <VocabWord> > FillVocabWordsByMaterial(Material material)
{
var arrayOfWords = material.File.Words == null
? new string[0]
: material.File.Words.Select(n => n.TheWord).ToArray();
return(await _vocabularyService.FillVocabByWords(arrayOfWords, User.Identity.GetUserId <int>()));
}