public static IMarcellEntity ToEntity(this LuceneDocument source, Type targetType)
 {
     if (targetType == typeof(MarcellDocument))
     {
         return(source.ToDocument());
     }
     else if (targetType == typeof(Section))
     {
         return(source.ToSection());
     }
     else if (targetType == typeof(Paragraph))
     {
         return(source.ToParagraph());
     }
     else if (targetType == typeof(Sentence))
     {
         return(source.ToSentence());
     }
     else
     {
         throw new InvalidOperationException("The requested type is unsupported!");
     }
 }