with the following:
{{   steps {}}
{{     withCredentials([}}
{{       string(credentialsId: params.GITHUB_PASSWORD, variable: 'GITHUB_PASSWORD'),}}
{{       string(credentialsId: params.GITHUB_APP_SECRET, variable: 'GITHUB_APP_SECRET')}}
    ]) {
      ansiblePlaybook(    {{      }}
        ...
      )
{{    }}}
{{  }}}

if param.GITHUB_PASSWORD is null (not defined), a NullPointerException is raised.

The code in com.cloudbees.plugins.credentials.CredentialsProvider.findCredentialById should check for null value of id and provide a more useful message than a stacktrace.