daniele

Doc: document the behavior of the if conditional when the field exists but is an empty string

3

**Description:** The [logstash documentation page](https://www.elastic.co/guide/en/logstash/current/event-dependent-configuration.html#conditionals) about the `if` syntax states: The expression `if [foo]` returns false when: - `[foo]` doesn’t exist in the event, - `[foo]` exists in the event,...