{||} cannot be used as a type

`{||}` cannot be used as a type.

**Expected behavior**

```fs

Microsoft (R) F# Interactive version 10.4.0 for F# 4.6
Copyright (c) Microsoft Corporation. All Rights Reserved.

For help type #help;;

> {||};;
val it : {||} = {}

> let x = {||};;
val x : {||} = {}

> let x : {||} = {||};;
val x : {||} = {}
```

**Repro steps and actual behavior**

```fs

Microsoft (R) F# Interactive version 10.4.0 for F# 4.6
Copyright (c) Microsoft Corporation. All Rights Reserved.

For help type #help;;

> {||};;
val it : {||} = {}

> let x = {||};;
val x : {||} = {}

> let x : {||} = {||};;

let x : {||} = {||};;
----------^^

stdin(3,11): error FS0010: Unexpected symbol '|}' in field declaration. Expected identifier or other token.
```

**Known workarounds**

Let the compiler infer the type.

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