Catch the case when the regex fails.

Jenkinsfile.groovy

@@ -173,7 +173,9 @@ String get_changelog(repo_name) {
 String extract(log_content, tag, gCube_release_version, component) {
 
     def matcher = "${log_content}" =~ /(?im)\[v${tag}\]\s\[r${gCube_release_version}\](.*)\[v.*\]\s\[r.*\]/
-    matcher.find()
+    if (!matcher.find()) {
+         return 'NA'
+    }
     assert matcher[0]: "Missing release notes for ${component}"
     return matcher[0]
 }