In Google's Cloud Logging query language, is it possible to query for the existence of a particular key in the `jsonPayload` dict?

E.g., suppose I know the `jsonPayload` will either be

```
{'keyA':'<some string>'}

```

or

```
{'keyB':'<some string'}

```

But I don't know what the `<some string>` will be. I want all logs that have the `keyB` key. I suppose I could test that for that key having a regex that includes everything, but is that the best/only way?