Error when closing dhall file in vscode.

To replicate:
Open VSCode with the extension running with any .dhall file open.
Close the tab for the .dhall file.
A "Output" tab pops up with this message:
```
..Dhall LSP Server has been started..
[Error - 10:38:56 PM] LSP: no handler for: SMethod_TextDocumentDidClose
```