Use ArgumentNullException.ThrowIfNull helper method

Did a simple search/replace on the whole repo (except the RSSDP project)
This reduces LOC and should improve performance (methods containing a throw statement don't get inlined)

```
if \((\w+) == null\)
\s+\{
\s+throw new ArgumentNullException\((.*)\);
\s+\}
```

```
ArgumentNullException.ThrowIfNull($1);
```

1 files changed, 1 insertions, 4 deletions

diff --git a/MediaBrowser.MediaEncoding/Attachments/AttachmentExtractor.cs b/MediaBrowser.MediaEncoding/Attachments/AttachmentExtractor.cs
index 142571e8f6..22abf93ac3 100644
--- a/MediaBrowser.MediaEncoding/Attachments/AttachmentExtractor.cs
+++ b/MediaBrowser.MediaEncoding/Attachments/AttachmentExtractor.cs
@@ -52,10 +52,7 @@ namespace MediaBrowser.MediaEncoding.Attachments
         /// <inheritdoc />
         public async Task<(MediaAttachment Attachment, Stream Stream)> GetAttachment(BaseItem item, string mediaSourceId, int attachmentStreamIndex, CancellationToken cancellationToken)
         {
-            if (item == null)
-            {
-                throw new ArgumentNullException(nameof(item));
-            }
+            ArgumentNullException.ThrowIfNull(item);
 
             if (string.IsNullOrWhiteSpace(mediaSourceId))
             {