Fix adding description in manageArtifacts

When description in null, we will add string to it and result will be
null<string>. This patch handles case when description is empty.

Related-Prod: PRODX-3456
Change-Id: I5b03937dfc7564f6e490baf647ab6eab352e409e
diff --git a/src/com/mirantis/mk/Workflow.groovy b/src/com/mirantis/mk/Workflow.groovy
index 8646073..67d61a8 100644
--- a/src/com/mirantis/mk/Workflow.groovy
+++ b/src/com/mirantis/mk/Workflow.groovy
@@ -1299,7 +1299,11 @@
         artifactoryRepo: "artifactory/${artifactoryRepoPath}",
     ]
     def artDescription = mcpArtifactory.uploadArtifactsToArtifactory(artConfig)
-    currentBuild.description += "${artDescription}<br>"
+    if (currentBuild.description) {
+        currentBuild.description += "${artDescription}<br>"
+    } else {
+        currentBuild.description = "${artDescription}<br>"
+    }
 
     junit(testResults: "${entrypointDirectory}/**/*.xml", allowEmptyResults: true)