JSON body webhook

Hai,
the receiverd json body via webhook is
{
evalMatches: [],
message: ‘TEST ALERT FOR K.’,
ruleId: 1,
ruleName: ‘PR alert’,
ruleUrl: ‘http://localhost:3000********1’,
state: ‘alerting’,
title: ‘[Alerting] PR alert’
}
The question is why this"evalMatches: [ ]" is empty… How can I add some data inside that ???
any help will be appreciated