I configured a job through the web UI, checked "SSH Agent" but didn't add any credentials. The saved `config.xml` file looks good:

<com.cloudbees.jenkins.plugins.sshagent.SSHAgentBuildWrapper plugin="ssh-agent@1.15">
  <credentialIds/>
  <ignoreMissing>false</ignoreMissing>  </com.cloudbees.jenkins.plugins.sshagent.SSHAgentBuildWrapper>

When opening the configure web UI again the form shows one credential entry. When saving the form now (without changing anything) the credential entry is being stored in the `config.xml`:

<com.cloudbees.jenkins.plugins.sshagent.SSHAgentBuildWrapper plugin="ssh-agent@1.15">
  <credentialIds>
    <string>xxxxx</string>
  </credentialIds>
  <ignoreMissing>false</ignoreMissing>  </com.cloudbees.jenkins.plugins.sshagent.SSHAgentBuildWrapper>

The expectation is that:

• if the `config.xml` doesn't contain a credential entry the web ui should not show one and
• opening the configure form and saving it without making any changes shouldn't add a credential entry