Rules Engine can be set up to evaluate the available fields in order to apply certain actions for the filtered orders. Sometimes, however, it may be needed to check if the order has a value present within a field. 

There are fields like Order Notes where there is already an option to evaluate the number of notes rather than their content. Setting it as in the below example will allow us to filter orders which do not have any notes:

Most of the other order fields do not have such a dedicated option, however, it is possible using the following method.

Let us say we want to park orders which do not have an email address.

We will use regex expression option to achieve this.

The following regular expression will be matched whenever there is at least one non-whitespace character within the field it evaluates:

(.|\s)*\S(.|\s)*

In our scenario we are after the opposite so we would use doesn't match any of (regex) option. The whole condition would look like this:

To sum up, depending on which regex comparator is selected, this regex expression can be used to either check for empty fields or fields which are not empty.