elasticsearch_exporter: Date parse error

Hi,

Here I am using this, I am getting this error,

level=error ts=2019-05-15T06:36:01.949096522Z caller=clusterinfo.go:171 msg="failed to retrieve cluster info from ES" err="parsing time \"\"Unknown\"\" as \"\"2006-01-02T15:04:05Z07:00\"\": cannot parse \"Unknown\"\" as \"2006\""