Formatting a polymorphic variant with an empty string name causes a syntax error

[tom-sherman]

Thank you for filing! Check list:

• Is it a bug? Usage questions should often be asked in the forum instead.
• Concise, focused, friendly issue title & description.
• A minimal, reproducible example.
• OS and browser versions, if relevant.
• Is it already fixed in master?

Steps to reproduce:

1. Format this code let x = #""

Expected behaviour:

Nothing or formatting applied

Actual behaviour:

"" is stripped leaving you with let x = # which is a syntax error.

[TheSpyder]

This probably belongs in the syntax repo, but I'm sure it'll be moved there when @bobzhang sees it.