# LibTmux.FSharp.Filter.isNull

- **Module:** LibTmux.FSharp
- **Package:** LibTmux.FSharp
- **Language:** F#
- **Kind:** function
- **Source:** https://github.com/libtmux/libtmux-dotnet/blob/cf34b255c896d19a97e7d7fabea58609c916012d/src/LibTmux.FSharp/Query.fsi#L42
- **Page:** https://libtmux.org/en/fsharp/latest/reference/libtmux-fsharp-filter-isnull/

```
val isNull: field: Field<'T, string> -> Filter<'T>
```

Matches a captured null string without treating an uncaptured field as absent.

## Parameters

- `field` (`Field<'T, string>`)