Fix existence checking in jenkins credential state

Change-Id: Id1536f7548e57d62b1268e9aef3cbac4e0d7d220
diff --git a/_states/jenkins_credential.py b/_states/jenkins_credential.py
index 23653fa..5df3278 100644
--- a/_states/jenkins_credential.py
+++ b/_states/jenkins_credential.py
@@ -21,7 +21,7 @@
   (it instanceof com.cloudbees.jenkins.plugins.sshcredentials.impl.BasicSSHUserPrivateKey &&
     it.username == "{username}" &&
     it.id == "{name}" &&
-    it.passphrase.toString() == "{password}" &&
+    ("{password}" == "" || it.passphrase.toString() == "{password}") &&
     it.description == "{desc}" &&
     it.privateKeySource.privateKey.equals(key.trim()))
 }}