How arguments could be checked

argumetscheck.cs

// ORIGINAL
   public async Task UploadBlobFromFile(string filePath, string containerName, string destinationPath)
        {
            if (!File.Exists(filePath))
            {
                throw new FileNotFoundException(filePath);
            }

            CloudBlobContainer container = await GetBlobContainer(containerName);
            CloudBlockBlob blob = GetBlockBlobReference(container, destinationPath);
            await blob.UploadFromFileAsync(filePath);
}

// NEW
   public async Task UploadBlobFromFile(string filePath, string containerName, string destinationPath)
        {
        if (filePath == null) 
                throw new ArgumentNullException(nameof(filePath), "Argument should be defined!");
        // OR
        if (string.IsNullOrEmpty(filePath)) 
                throw new ArgumentException("Argument should be defined!", nameof(filePath));
        
            if (!File.Exists(filePath))
            {
                throw new FileNotFoundException(filePath);
            }

            CloudBlobContainer container = await GetBlobContainer(containerName);
            CloudBlockBlob blob = GetBlockBlobReference(container, destinationPath);
            await blob.UploadFromFileAsync(filePath);
}


// The same with annotations
using JetBrains.Annotations;

   public async Task UploadBlobFromFile([NotNull] string filePath, [NotNull] string containerName, string destinationPath)
  {
        if (filePath == null) 
                throw new ArgumentNullException(nameof(filePath), "Argument should be defined!");
        // OR
        if (string.IsNullOrEmpty(filePath)) 
                throw new ArgumentException("Argument should be defined!", nameof(filePath));
        
  }